diff --git a/.editorconfig b/.editorconfig
index 7382bb8eb572..4d8854436cb8 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -13,3 +13,7 @@ trim_trailing_whitespace = true
 
 [*.{yml,yaml}]
 indent_size = 2
+
+# Two trailing spaces are a hard line break in the converted pages.
+[docs/**.md]
+trim_trailing_whitespace = false
diff --git a/.gitattributes b/.gitattributes
index 0ec474bf866d..ed268a11ca73 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -36,5 +36,7 @@ AGENTS.md                    export-ignore
 
 # source user guide
 user_guide_src/ export-ignore
+docs/           export-ignore
+mkdocs.yml      export-ignore
 .nojekyll       export-ignore
 phpdoc.dist.xml export-ignore
diff --git a/.github/workflows/test-userguide.yml b/.github/workflows/test-userguide.yml
index b7ef79e0170d..6cbc34d341a8 100644
--- a/.github/workflows/test-userguide.yml
+++ b/.github/workflows/test-userguide.yml
@@ -1,13 +1,18 @@
 # When a Pull Request is opened that modifies
 # the User Guide source, build the User Guide
-# with Sphinx and let the contributor know of
-# any errors.
+# with Sphinx or MkDocs and let the contributor
+# know of any errors.
 name: Test User Guide
 
 on:
   pull_request:
     paths:
       - 'user_guide_src/**'
+      - 'docs/**'
+      - 'mkdocs.yml'
+      - 'admin/anchors.py'
+      - 'admin/llms.py'
+      - 'admin/update-docs-nav.php'
       - '.github/workflows/test-userguide.yml'
 
 concurrency:
@@ -42,3 +47,42 @@ jobs:
       - name: Build Docs with Sphinx
         run: make html SPHINXOPTS="-W --keep-going -w /tmp/sphinx-log"
         working-directory: user_guide_src
+
+  markdown_check:
+    name: Check Markdown User Guide
+    runs-on: ubuntu-24.04
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@eb7c497e18156a6bbabfef1d3a82760b9eda3962 # 2.40.0
+        with:
+          php-version: '8.2'
+          coverage: none
+
+      - name: Setup Python
+        uses: actions/setup-python@6d4fd22b20465ccc0f7354476588e8df7c9ca0e0 # v7.1.0
+        with:
+          python-version: '3.12'
+
+      - name: Install MkDocs
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r docs/requirements.txt
+
+      - name: Check that every page is in the nav
+        run: php admin/update-docs-nav.php --check
+
+      - name: Build Docs with MkDocs
+        env:
+          NO_MKDOCS_2_WARNING: '1'
+        run: mkdocs build --strict
+
+      - name: Write the llms files and the anchor aliases
+        run: |
+          python admin/llms.py
+          python admin/anchors.py
diff --git a/.gitignore b/.gitignore
index 3e4a7c1d18f7..418eb60af297 100644
--- a/.gitignore
+++ b/.gitignore
@@ -75,6 +75,9 @@ php_errors.log
 # User Guide Temp Files
 #-------------------------
 /user_guide_src/build/*
+/site/
+/venv/
+__pycache__/
 
 #-------------------------
 # Test Files
diff --git a/admin/anchors.py b/admin/anchors.py
new file mode 100644
index 000000000000..37a533abfca5
--- /dev/null
+++ b/admin/anchors.py
@@ -0,0 +1,42 @@
+"""Adds the legacy anchor ids listed in the docs' .anchors.json to the headings of the built site."""
+
+from __future__ import annotations
+
+import html
+import json
+import re
+import sys
+from pathlib import Path
+
+from llms import load
+
+
+def main(config_path: Path) -> None:
+    config = load(config_path)
+    base = config_path.parent
+    docs = base / config.get("docs_dir", "docs")
+    site = base / config.get("site_dir", "site")
+    aliases = json.loads((docs / ".anchors.json").read_text(encoding="utf-8"))
+
+    for page, headings in aliases.items():
+        target = site / (page.removesuffix(".md") + ".html")
+
+        if not target.is_file():
+            print(f"WARNING - {page} has aliases but was not built", file=sys.stderr)
+            continue
+
+        content = target.read_text(encoding="utf-8")
+
+        for heading, ids in headings.items():
+            opening = re.compile(rf'(<h[1-6]\b[^>]*\bid="{re.escape(html.escape(heading))}"[^>]*>)')
+            anchors = "".join(f'<a id="{html.escape(id_)}"></a>' for id_ in ids)
+            content, count = opening.subn(lambda match: match.group(1) + anchors, content, count=1)
+
+            if count == 0:
+                print(f"WARNING - {page} has no heading #{heading} for its aliases", file=sys.stderr)
+
+        target.write_text(content, encoding="utf-8")
+
+
+if __name__ == "__main__":
+    main(Path(sys.argv[1] if len(sys.argv) > 1 else "mkdocs.yml"))
diff --git a/admin/llms.py b/admin/llms.py
new file mode 100644
index 000000000000..5dae2c1dd465
--- /dev/null
+++ b/admin/llms.py
@@ -0,0 +1,95 @@
+"""Writes llms.txt, llms-full.txt and each page's Markdown beside its HTML in the built site."""
+
+from __future__ import annotations
+
+import re
+import sys
+from pathlib import Path
+
+import yaml
+
+
+class Loader(yaml.SafeLoader):
+    pass
+
+
+Loader.add_multi_constructor("!", lambda loader, suffix, node: None)
+
+
+def load(path: Path) -> dict:
+    return yaml.load(path.read_text(encoding="utf-8"), Loader=Loader) or {}
+
+
+def title_of(markdown: Path) -> str:
+    fenced = False
+
+    for line in markdown.read_text(encoding="utf-8").splitlines():
+        if line.startswith("```"):
+            fenced = not fenced
+        elif not fenced and (match := re.match(r"# (.+?)\s*#*\s*$", line)):
+            return match.group(1)
+
+    return markdown.stem
+
+
+def index_lines(items: list, docs: Path, depth: int = 0) -> list[str]:
+    indent = "    " * max(depth - 1, 0)
+    lines: list[str] = []
+
+    for item in items:
+        title, target = next(iter(item.items())) if isinstance(item, dict) else (None, item)
+
+        if isinstance(target, list):
+            lines += ["", f"## {title}", ""] if depth == 0 else [f"{indent}- {title}"]
+            lines += index_lines(target, docs, depth + 1)
+        elif isinstance(target, str) and target.endswith(".md"):
+            lines.append(f"{indent}- [{title or title_of(docs / target)}]({target})")
+
+    return lines
+
+
+def nav_pages(items: list) -> list[str]:
+    pages: list[str] = []
+
+    for item in items:
+        target = next(iter(item.values())) if isinstance(item, dict) else item
+
+        if isinstance(target, list):
+            pages += nav_pages(target)
+        elif isinstance(target, str) and target.endswith(".md"):
+            pages.append(target)
+
+    return pages
+
+
+def main(config_path: Path) -> None:
+    config = load(config_path)
+    base = config_path.parent
+    nav = config.get("nav") or load(base / config["INHERIT"]).get("nav", [])
+    docs = base / config.get("docs_dir", "docs")
+    site = base / config.get("site_dir", "site")
+
+    in_nav = nav_pages(nav)
+    outside_nav = sorted(
+        path.relative_to(docs).as_posix() for path in docs.rglob("*.md") if path.relative_to(docs).as_posix() not in in_nav
+    )
+    pages = in_nav + outside_nav
+
+    for page in pages:
+        (site / page).write_text((docs / page).read_text(encoding="utf-8"), encoding="utf-8")
+
+    index = [f"# {config['site_name']}", "", f"> {config['site_description']}", "", *index_lines(nav, docs)]
+
+    if outside_nav:
+        index += ["", "## Other pages", ""]
+        index += [f"- [{title_of(docs / page)}]({page})" for page in outside_nav]
+
+    (site / "llms.txt").write_text("\n".join(index) + "\n", encoding="utf-8")
+    (site / "llms-full.txt").write_text(
+        "\n\n".join((docs / page).read_text(encoding="utf-8").strip() for page in pages) + "\n",
+        encoding="utf-8",
+    )
+
+
+if __name__ == "__main__":
+    main(Path(sys.argv[1] if len(sys.argv) > 1 else "mkdocs.yml"))
diff --git a/admin/update-docs-nav.php b/admin/update-docs-nav.php
new file mode 100644
index 000000000000..33ecfa89613b
--- /dev/null
+++ b/admin/update-docs-nav.php
@@ -0,0 +1,246 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of CodeIgniter 4 framework.
+ *
+ * (c) CodeIgniter Foundation <admin@codeigniter.com>
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+/**
+ * Adds the pages of the user guide that are missing from its nav (docs/.nav.yml).
+ *
+ * A page goes into the section whose first page links to it, after the page
+ * that precedes it in that list. With --check, nothing is changed, and the
+ * script exits with 1 when a page is missing or a nav entry has no file.
+ *
+ * Usage: php admin/update-docs-nav.php [--check] [--docs=<directory>]
+ */
+
+/**
+ * @return list<string> Markdown pages under $docs, relative to it
+ */
+function docs_pages(string $docs): array
+{
+    $pages    = [];
+    $iterator = new RecursiveIteratorIterator(
+        new RecursiveDirectoryIterator($docs, FilesystemIterator::SKIP_DOTS),
+    );
+
+    foreach ($iterator as $file) {
+        $page = str_replace('\\', '/', substr($file->getPathname(), strlen($docs) + 1));
+
+        if ($file->getExtension() === 'md' && ! str_starts_with($page, 'overrides/')) {
+            $pages[] = $page;
+        }
+    }
+
+    sort($pages);
+
+    return $pages;
+}
+
+/**
+ * @param list<string> $lines
+ *
+ * @return array{indent: int, page: string|null, section: bool}|null
+ */
+function parse_nav_line(array $lines, int $i): ?array
+{
+    if (preg_match('/^(\s*)- (?:(?:"[^"]*"|[^:]+): )?([^\s:]+\.md)\s*$/', $lines[$i], $matches) === 1) {
+        return ['indent' => strlen($matches[1]), 'page' => $matches[2], 'section' => false];
+    }
+
+    if (preg_match('/^(\s*)- (?:"[^"]*"|[^:]+):\s*$/', $lines[$i], $matches) === 1) {
+        $head = isset($lines[$i + 1]) ? parse_nav_line($lines, $i + 1) : null;
+
+        return ['indent' => strlen($matches[1]), 'page' => $head['page'] ?? null, 'section' => true];
+    }
+
+    return null;
+}
+
+/**
+ * @param list<string> $lines
+ *
+ * @return list<string>
+ */
+function nav_pages(array $lines): array
+{
+    $pages = [];
+
+    foreach (array_keys($lines) as $i) {
+        $entry = parse_nav_line($lines, $i);
+
+        if ($entry !== null && ! $entry['section']) {
+            $pages[] = $entry['page'];
+        }
+    }
+
+    return $pages;
+}
+
+/**
+ * @return list<string> Pages that $page links to, in order, as paths relative to $docs
+ */
+function linked_pages(string $docs, string $page): array
+{
+    preg_match_all('/\]\(([^)#\s]+\.md)(?:#[^)]*)?\)/', (string) file_get_contents($docs . '/' . $page), $matches);
+
+    $links = [];
+
+    foreach ($matches[1] as $link) {
+        if (str_contains($link, '://')) {
+            continue;
+        }
+
+        $parts = [];
+
+        foreach (explode('/', dirname($page) . '/' . $link) as $part) {
+            if ($part === '..') {
+                array_pop($parts);
+            } elseif ($part !== '.' && $part !== '') {
+                $parts[] = $part;
+            }
+        }
+
+        $links[] = implode('/', $parts);
+    }
+
+    return array_values(array_unique($links));
+}
+
+/**
+ * The index of the last line of the entry at $i, including the entries nested in it.
+ *
+ * @param list<string> $lines
+ */
+function entry_end(array $lines, int $i): int
+{
+    $indent = parse_nav_line($lines, $i)['indent'];
+    $end    = $i;
+
+    for ($j = $i + 1; $j < count($lines); $j++) {
+        $entry = parse_nav_line($lines, $j);
+
+        if ($entry === null || $entry['indent'] <= $indent) {
+            break;
+        }
+
+        $end = $j;
+    }
+
+    return $end;
+}
+
+/**
+ * Inserts $page into $lines, returning the title of the section it went into, or null when no section links to it.
+ *
+ * @param list<string> $lines
+ */
+function insert_page(array &$lines, string $docs, string $page): ?string
+{
+    $target = null;
+
+    foreach (array_keys($lines) as $i) {
+        $section = parse_nav_line($lines, $i);
+
+        if ($section === null || ! $section['section'] || $section['page'] === null) {
+            continue;
+        }
+
+        if (! in_array($page, linked_pages($docs, $section['page']), true)) {
+            continue;
+        }
+
+        // The index of an outer section also lists the pages of the sections nested in it.
+        if ($target === null || $section['indent'] > $target['indent']) {
+            $target = $section + ['line' => $i];
+        }
+    }
+
+    if ($target === null) {
+        return null;
+    }
+
+    $order       = linked_pages($docs, $target['page']);
+    $position    = array_search($page, $order, true);
+    $after       = $target['line'] + 1;
+    $childIndent = $target['indent'] + 4;
+    $end         = entry_end($lines, $target['line']);
+
+    for ($j = $target['line'] + 1; $j <= $end; $j++) {
+        $entry = parse_nav_line($lines, $j);
+
+        if ($entry === null || $entry['indent'] !== $childIndent || $entry['page'] === null) {
+            continue;
+        }
+
+        $before = array_search($entry['page'], $order, true);
+
+        if ($j === $target['line'] + 1 || ($before !== false && $before < $position)) {
+            $after = entry_end($lines, $j);
+        }
+    }
+
+    array_splice($lines, $after + 1, 0, [str_repeat(' ', $childIndent) . '- ' . $page]);
+
+    return $target['page'];
+}
+
+$check = in_array('--check', $argv, true);
+$docs  = 'docs';
+
+foreach ($argv as $argument) {
+    if (str_starts_with($argument, '--docs=')) {
+        $docs = rtrim(substr($argument, strlen('--docs=')), '/');
+    }
+}
+
+$navFile = $docs . '/.nav.yml';
+
+if (! is_file($navFile)) {
+    echo "{$navFile} is not found.\n";
+
+    exit(1);
+}
+
+$lines   = explode("\n", rtrim((string) file_get_contents($navFile), "\n"));
+$pages   = docs_pages($docs);
+$missing = array_values(array_diff($pages, nav_pages($lines)));
+$stale   = array_values(array_diff(nav_pages($lines), $pages));
+
+foreach ($stale as $page) {
+    echo "The nav lists {$page}, which does not exist.\n";
+}
+
+foreach ($missing as $page) {
+    if ($check) {
+        echo "{$page} is missing from the nav.\n";
+
+        continue;
+    }
+
+    $section = insert_page($lines, $docs, $page);
+
+    if ($section === null) {
+        $lines[] = '  - ' . $page;
+        echo "Added {$page} at the end of the nav, since no section links to it. Move it by hand.\n";
+    } else {
+        echo "Added {$page} to the section of {$section}.\n";
+    }
+}
+
+if (! $check && $missing !== []) {
+    file_put_contents($navFile, implode("\n", $lines) . "\n");
+}
+
+if ($check && ($missing !== [] || $stale !== [])) {
+    echo "Run \"php admin/update-docs-nav.php\" to update docs/.nav.yml.\n";
+}
+
+exit($check && ($missing !== [] || $stale !== []) ? 1 : 0);
diff --git a/docs/overrides/assets/css/code.css b/docs/overrides/assets/css/code.css
new file mode 100644
index 000000000000..f9ec92f50951
--- /dev/null
+++ b/docs/overrides/assets/css/code.css
@@ -0,0 +1,98 @@
+/* The theme turns ligatures off in code. */
+.md-typeset code,
+.md-typeset pre {
+    font-variant-ligatures: normal;
+}
+
+/* Pygments marks most PHP identifiers Name.Other, which the theme leaves at body color. */
+.highlight .nx {
+    color: var(--md-code-hl-function-color);
+}
+
+/* Light-scheme code colors matched to VS Code's Light Modern token palette, on the theme's own background. */
+[data-md-color-scheme="codeigniter"] {
+    --md-code-fg-color: #3b3b3b;
+    --md-code-hl-keyword-color: #0000ff;
+    --md-code-hl-function-color: #795e26;
+    --md-code-hl-string-color: #a31515;
+    --md-code-hl-number-color: #098658;
+    --md-code-hl-comment-color: #008000;
+    --md-code-hl-variable-color: #001080;
+    --md-code-hl-operator-color: #3b3b3b;
+    --md-code-hl-punctuation-color: #3b3b3b;
+    --md-code-hl-constant-color: #0070c1;
+    --md-code-hl-name-color: #3b3b3b;
+    --md-code-hl-special-color: #811f3f;
+}
+
+[data-md-color-scheme="codeigniter"] .highlight .nc,
+[data-md-color-scheme="codeigniter"] .highlight .nn,
+[data-md-color-scheme="codeigniter"] .highlight .nx.nx-class {
+    color: #267f99;
+}
+
+[data-md-color-scheme="codeigniter"] .highlight .si {
+    color: #001080;
+}
+
+[data-md-color-scheme="codeigniter"] .highlight .k.k-control {
+    color: #af00db;
+}
+
+[data-md-color-scheme="codeigniter"] .highlight .nv.nv-this {
+    color: #0000ff;
+}
+
+[data-md-color-scheme="codeigniter"] .highlight .nx.nx-constant {
+    color: #0070c1;
+}
+
+[data-md-color-scheme="codeigniter"] .highlight .na.na-call {
+    color: #795e26;
+}
+
+/* Dark-scheme code colors matched to VS Code's Dark Modern token palette. */
+[data-md-color-scheme="slate"] {
+    --md-code-bg-color: #1f1f1f;
+    --md-code-fg-color: #cccccc;
+    --md-code-hl-keyword-color: #569cd6;
+    --md-code-hl-function-color: #dcdcaa;
+    --md-code-hl-string-color: #ce9178;
+    --md-code-hl-number-color: #b5cea8;
+    --md-code-hl-comment-color: #6a9955;
+    --md-code-hl-variable-color: #9cdcfe;
+    --md-code-hl-operator-color: #d4d4d4;
+    --md-code-hl-punctuation-color: #d4d4d4;
+    --md-code-hl-constant-color: #569cd6;
+    --md-code-hl-name-color: #cccccc;
+    --md-code-hl-special-color: #d16969;
+}
+
+[data-md-color-scheme="slate"] .highlight .nc,
+[data-md-color-scheme="slate"] .highlight .nn {
+    color: #4ec9b0;
+}
+
+[data-md-color-scheme="slate"] .highlight .si {
+    color: #9cdcfe;
+}
+
+[data-md-color-scheme="slate"] .highlight .k.k-control {
+    color: #c586c0;
+}
+
+[data-md-color-scheme="slate"] .highlight .nv.nv-this {
+    color: #569cd6;
+}
+
+[data-md-color-scheme="slate"] .highlight .nx.nx-class {
+    color: #4ec9b0;
+}
+
+[data-md-color-scheme="slate"] .highlight .nx.nx-constant {
+    color: #9cdcfe;
+}
+
+[data-md-color-scheme="slate"] .highlight .na.na-call {
+    color: #dcdcaa;
+}
diff --git a/docs/overrides/assets/css/codeigniter.css b/docs/overrides/assets/css/codeigniter.css
new file mode 100644
index 000000000000..c63734fefead
--- /dev/null
+++ b/docs/overrides/assets/css/codeigniter.css
@@ -0,0 +1,172 @@
+[data-md-color-scheme="codeigniter"] {
+    --md-primary-fg-color:        #dd4814;
+    --md-primary-fg-color--light: #ECB7B7;
+    --md-primary-fg-color--dark:  #90030C;
+
+    --md-default-bg-color: #fcfcfc;
+
+    --md-typeset-a-color: #e74c3c;
+    --md-accent-fg-color: #97310e;
+
+    --md-accent-fg-color--transparent: #ECB7B7;
+
+    /* Enhanced heading styles for better visibility */
+    .md-typeset h1 {
+        font-weight: 700;
+        color: #1a202c;
+        border-bottom: 2px solid #dd4814;
+        padding-bottom: 0.3em;
+    }
+
+    .md-typeset h2 {
+        font-weight: 600;
+        color: #2d3748;
+        border-bottom: 1px solid #cbd5e0;
+        padding-bottom: 0.2em;
+    }
+
+    .md-typeset h3 {
+        font-weight: 600;
+        color: #1a202c;
+    }
+
+    .md-typeset h4 {
+        font-weight: 600;
+        color: #2d3748;
+    }
+
+    .md-typeset h5 {
+        text-transform: none;
+        font-weight: 600;
+        color: #1a202c;
+    }
+
+    .md-typeset h6 {
+        font-weight: 600;
+        color: #2d3748;
+    }
+
+    /* Inline code styling - orange color like links */
+    .md-typeset p code,
+    .md-typeset li code,
+    .md-typeset td code,
+    .md-typeset th code {
+        border: 1px solid #e1e4e5;
+        color: #e74c3c; /* Same orange color as links */
+    }
+
+    /* Code blocks should keep default styling */
+    .md-typeset pre code {
+        border: none;
+    }
+
+    .md-typeset .admonition.important,
+    .md-typeset details.important {
+        border-color: #dd4814;
+    }
+
+    .md-typeset .important > .admonition-title,
+    .md-typeset .important > summary {
+        background-color: #dd4814;
+        color: white;
+    }
+
+    .md-typeset .important > .admonition-title:before,
+    .md-typeset .important > summary:before {
+        background-color: white;
+        -webkit-mask-image: var(--md-admonition-icon--warning);
+        mask-image: var(--md-admonition-icon--warning);
+    }
+
+    /* Note admonition styling */
+    .md-typeset .admonition.note,
+    .md-typeset details.note {
+        border-color: #448aff;
+    }
+
+    .md-typeset .note > .admonition-title,
+    .md-typeset .note > summary {
+        background-color: #448aff;
+        color: white;
+    }
+
+    .md-typeset .note > .admonition-title:before,
+    .md-typeset .note > summary:before {
+        background-color: white;
+        -webkit-mask-image: var(--md-admonition-icon--note);
+        mask-image: var(--md-admonition-icon--note);
+    }
+
+    /* Warning admonition styling */
+    .md-typeset .admonition.warning,
+    .md-typeset details.warning {
+        border-color: #ff9800;
+    }
+
+    .md-typeset .warning > .admonition-title,
+    .md-typeset .warning > summary {
+        background-color: #ff9800;
+        color: white;
+    }
+
+    .md-typeset .warning > .admonition-title:before,
+    .md-typeset .warning > summary:before {
+        background-color: white;
+        -webkit-mask-image: var(--md-admonition-icon--warning);
+        mask-image: var(--md-admonition-icon--warning);
+    }
+
+    /* Image styling for better visibility in light mode */
+    .md-typeset img {
+        border-color: #d1d4d8;
+        box-shadow: 0 2px 6px rgba(0, 0, 0, 0.2);
+    }
+
+    /* Remove the shadow from inline images or icons */
+    .md-typeset p img[src*="icon"],
+    .md-typeset p img[width="16"],
+    .md-typeset p img[width="24"],
+    .md-typeset p img[height="16"],
+    .md-typeset p img[height="24"] {
+        box-shadow: none;
+    }
+
+    /* Table of Contents list styling */
+    .md-typeset ul li {
+        margin-bottom: 0; /* Reduce vertical spacing between list items */
+        margin-top: 0;
+    }
+
+    /* Nested list bullet styles */
+    .md-typeset ul {
+        list-style-type: disc; /* Top level uses solid disc */
+    }
+
+    .md-typeset ul ul {
+        list-style-type: circle; /* Second level uses outline circle */
+    }
+
+    .md-typeset ul ul ul {
+        list-style-type: square; /* Third level uses square */
+    }
+
+    /* Additional spacing adjustments for nested lists */
+    .md-typeset ul ul {
+        margin-top: 0;
+        margin-bottom: 0;
+    }
+
+    /* Navigation adjustments for better spacing in dark mode */
+
+    .md-nav[aria-expanded="true"] {
+        margin-bottom: 0.5rem !important;
+    }
+
+    .md-nav .md-nav .md-nav__list {
+        padding-left: 1.2rem !important;
+    }
+
+    .md-nav__item {
+        line-height: 1.4 !important;
+    }
+}
diff --git a/docs/overrides/assets/css/codeigniter_dark_mode.css b/docs/overrides/assets/css/codeigniter_dark_mode.css
new file mode 100644
index 000000000000..8300abecae2d
--- /dev/null
+++ b/docs/overrides/assets/css/codeigniter_dark_mode.css
@@ -0,0 +1,150 @@
+[data-md-color-scheme="slate"] {
+    --md-primary-fg-color: #b13a10;
+    --md-primary-fg-color--light: #8d7474;
+    --md-primary-fg-color--dark: #6d554d;
+
+    --md-default-bg-color: #1e2129;
+
+    --md-typeset-a-color: #ed6436;
+    --md-accent-fg-color: #f18a67;
+
+    --md-accent-fg-color--transparent: #625151;
+
+    /* Enhanced heading styles for better visibility in dark mode */
+    .md-typeset h1 {
+        font-weight: 700;
+        color: #f8f9fa;
+        border-bottom: 2px solid #ed6436;
+        padding-bottom: 0.3em;
+    }
+
+    .md-typeset h2 {
+        font-weight: 600;
+        color: #e9ecef;
+        border-bottom: 1px solid #495057;
+        padding-bottom: 0.2em;
+    }
+
+    .md-typeset h3 {
+        font-weight: 600;
+        color: #f8f9fa;
+    }
+
+    .md-typeset h4 {
+        font-weight: 600;
+        color: #e9ecef;
+    }
+
+    .md-typeset h5 {
+        text-transform: none;
+        font-weight: 600;
+        color: #f8f9fa;
+    }
+
+    .md-typeset h6 {
+        font-weight: 600;
+        color: #e9ecef;
+    }
+
+    /* Inline code styling - orange color like links */
+    .md-typeset p code,
+    .md-typeset li code,
+    .md-typeset td code,
+    .md-typeset th code {
+        border: 1px solid #3f4547;
+        color: #ed6436; /* Same orange color as links */
+    }
+
+    /* Code blocks should keep default styling */
+    .md-typeset pre code {
+        border: none;
+    }
+
+    .md-typeset .admonition.note,
+    .md-typeset details.note {
+        border-color: #2c5293;
+    }
+
+    .md-typeset .note > .admonition-title:before,
+    .md-typeset .note > summary:before {
+        background-color: #2c5293;
+        -webkit-mask-image: var(--md-admonition-icon--note);
+        mask-image: var(--md-admonition-icon--note);
+    }
+
+    .md-typeset .admonition.warning,
+    .md-typeset details.warning {
+        border-color: #97631e;
+    }
+
+    .md-typeset .warning > .admonition-title:before,
+    .md-typeset .warning > summary:before {
+        background-color: #97631e;
+        -webkit-mask-image: var(--md-admonition-icon--warning);
+        mask-image: var(--md-admonition-icon--warning);
+    }
+
+    .md-typeset .admonition.important,
+    .md-typeset details.important {
+        border-color: #8a3111;
+    }
+
+    .md-typeset .important > .admonition-title:before,
+    .md-typeset .important > summary:before {
+        background-color: #8a3111;
+        -webkit-mask-image: var(--md-admonition-icon--warning);
+        mask-image: var(--md-admonition-icon--warning);
+    }
+
+    .md-typeset .admonition.success,
+    .md-typeset details.success {
+        border-color: #026f2f;
+    }
+
+    .md-typeset .success > .admonition-title:before,
+    .md-typeset .success > summary:before {
+        background-color: #026f2f;
+        -webkit-mask-image: var(--md-admonition-icon--success);
+        mask-image: var(--md-admonition-icon--success);
+    }
+
+    /* Table of Contents list styling for dark mode */
+    .md-typeset ul li {
+        margin-bottom: 0; /* Reduce vertical spacing between list items */
+        margin-top: 0;
+    }
+
+    /* Nested list bullet styles */
+    .md-typeset ul {
+        list-style-type: disc; /* Top level uses solid disc */
+    }
+
+    .md-typeset ul ul {
+        list-style-type: circle; /* Second level uses outline circle */
+    }
+
+    .md-typeset ul ul ul {
+        list-style-type: square; /* Third level uses square */
+    }
+
+    /* Additional spacing adjustments for nested lists */
+    .md-typeset ul ul {
+        margin-top: 0;
+        margin-bottom: 0;
+    }
+
+    /* Navigation adjustments for better spacing in dark mode */
+
+    .md-nav[aria-expanded="true"] {
+        margin-bottom: 0.5rem !important;
+    }
+
+    .md-nav .md-nav .md-nav__list {
+        padding-left: 1.2rem !important;
+        /* background-color: rgba(245,245,255,0.01) !important; */
+    }
+
+    .md-nav__item {
+        line-height: 1.4 !important;
+    }
+}
diff --git a/docs/overrides/assets/css/fonts.css b/docs/overrides/assets/css/fonts.css
new file mode 100644
index 000000000000..045da829045d
--- /dev/null
+++ b/docs/overrides/assets/css/fonts.css
@@ -0,0 +1,94 @@
+@font-face {
+    font-family: "Inter";
+    font-style: normal;
+    font-weight: 300;
+    font-display: swap;
+    src: url("../fonts/Inter/inter-latin-300-normal.woff2") format("woff2");
+    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
+@font-face {
+    font-family: "Inter";
+    font-style: italic;
+    font-weight: 300;
+    font-display: swap;
+    src: url("../fonts/Inter/inter-latin-300-italic.woff2") format("woff2");
+    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
+@font-face {
+    font-family: "Inter";
+    font-style: normal;
+    font-weight: 400;
+    font-display: swap;
+    src: url("../fonts/Inter/inter-latin-400-normal.woff2") format("woff2");
+    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
+@font-face {
+    font-family: "Inter";
+    font-style: italic;
+    font-weight: 400;
+    font-display: swap;
+    src: url("../fonts/Inter/inter-latin-400-italic.woff2") format("woff2");
+    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
+@font-face {
+    font-family: "Inter";
+    font-style: normal;
+    font-weight: 700;
+    font-display: swap;
+    src: url("../fonts/Inter/inter-latin-700-normal.woff2") format("woff2");
+    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
+@font-face {
+    font-family: "Inter";
+    font-style: italic;
+    font-weight: 700;
+    font-display: swap;
+    src: url("../fonts/Inter/inter-latin-700-italic.woff2") format("woff2");
+    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
+@font-face {
+    font-family: "JetBrains Mono";
+    font-style: normal;
+    font-weight: 400;
+    font-display: swap;
+    src: url("../fonts/JetBrainsMono/jetbrains-mono-latin-400-normal.woff2") format("woff2");
+    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
+@font-face {
+    font-family: "JetBrains Mono";
+    font-style: italic;
+    font-weight: 400;
+    font-display: swap;
+    src: url("../fonts/JetBrainsMono/jetbrains-mono-latin-400-italic.woff2") format("woff2");
+    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
+@font-face {
+    font-family: "JetBrains Mono";
+    font-style: normal;
+    font-weight: 700;
+    font-display: swap;
+    src: url("../fonts/JetBrainsMono/jetbrains-mono-latin-700-normal.woff2") format("woff2");
+    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
+@font-face {
+    font-family: "JetBrains Mono";
+    font-style: italic;
+    font-weight: 700;
+    font-display: swap;
+    src: url("../fonts/JetBrainsMono/jetbrains-mono-latin-700-italic.woff2") format("woff2");
+    unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
+}
+
+:root {
+    --md-text-font: "Inter";
+    --md-code-font: "JetBrains Mono";
+}
diff --git a/docs/overrides/assets/css/layout.css b/docs/overrides/assets/css/layout.css
new file mode 100644
index 000000000000..e276fd18d2e3
--- /dev/null
+++ b/docs/overrides/assets/css/layout.css
@@ -0,0 +1,153 @@
+/* Search field and its shortcut hint */
+.md-search__form {
+    border-radius: .4rem;
+}
+
+[data-md-toggle="search"]:checked ~ .md-header .md-search__form {
+    border-radius: .4rem .4rem 0 0;
+}
+
+.md-search__output {
+    border-radius: 0 0 .4rem .4rem;
+}
+
+@media screen and (min-width: 60em) {
+    .md-search__form {
+        background-color: #ffffff1f;
+    }
+
+    .md-search__form:hover {
+        background-color: #00000042;
+    }
+}
+
+.md-search__form[data-shortcut]::after {
+    content: attr(data-shortcut);
+    position: absolute;
+    top: 50%;
+    right: .6rem;
+    z-index: 2;
+    padding: 0 .3rem;
+    border: .05rem solid currentColor;
+    border-radius: .2rem;
+    color: var(--md-primary-bg-color--light);
+    font-size: .6rem;
+    line-height: 1.4;
+    pointer-events: none;
+    transform: translateY(-50%);
+}
+
+[data-md-toggle="search"]:checked ~ .md-header .md-search__form::after {
+    display: none;
+}
+
+/* Wider content column */
+.md-grid {
+    max-width: 71.4rem;
+}
+
+.md-sidebar--secondary {
+    width: 13rem;
+}
+
+/* Translucent header */
+.md-header {
+    background-color: color-mix(in srgb, var(--md-primary-fg-color) 85%, transparent);
+    -webkit-backdrop-filter: blur(.4rem);
+    backdrop-filter: blur(.4rem);
+}
+
+/* Labelled edit button */
+.md-typeset .md-content__button--labelled {
+    display: inline-flex;
+    gap: .3rem;
+    align-items: center;
+    padding: .2rem .6rem;
+    border-radius: .4rem;
+    background-color: var(--md-default-fg-color--lightest);
+    color: var(--md-default-fg-color--light);
+    font-size: .7rem;
+}
+
+.md-typeset .md-content__button--labelled:hover {
+    background-color: var(--md-accent-fg-color--transparent);
+    color: var(--md-accent-fg-color);
+}
+
+/* Smaller previous and next links */
+.md-footer__title {
+    font-size: .8rem;
+}
+
+.md-footer__direction {
+    font-size: .6rem;
+}
+
+.md-sidebar--secondary .md-nav .md-nav .md-nav__list {
+    padding-left: .6rem !important;
+}
+
+/* The version list opens on click, not on the theme's hover or focus. */
+.md-version:hover .md-version__list,
+.md-version:focus-within .md-version__list {
+    animation: none;
+    max-height: 0;
+    opacity: 0;
+}
+
+.md-version {
+    font-size: .7rem;
+    position: relative;
+}
+
+.md-version__item {
+    line-height: 1.5rem;
+}
+
+/* Lets the title shrink on narrow screens instead of pushing the header's buttons off screen. */
+.md-header__title {
+    min-width: 0;
+}
+
+.md-version__current {
+    line-height: 2.4rem;
+    margin: 0 .4rem;
+    white-space: nowrap;
+}
+
+.md-version__list {
+    margin: 0;
+    right: 0;
+    top: 2.2rem;
+    visibility: hidden;
+}
+
+.md-version.md-version--open .md-version__list {
+    max-height: 10rem;
+    opacity: 1;
+    visibility: visible;
+}
+
+/* A transparent border keeps images the same size in the scheme without a visible one. */
+.md-typeset img {
+    border: 1px solid transparent;
+    border-radius: 6px;
+    height: auto;
+    margin: .5rem 0;
+    max-width: 100%;
+}
+
+.md-typeset p img[src*="icon"],
+.md-typeset p img[width="16"],
+.md-typeset p img[width="24"],
+.md-typeset p img[height="16"],
+.md-typeset p img[height="24"] {
+    border: none;
+    border-radius: 0;
+    margin: 0;
+}
+
+/* Keeps the footer below the first screen, so short and long pages scroll alike. */
+.md-main {
+    min-height: 100vh;
+}
diff --git a/docs/overrides/assets/favicon.ico b/docs/overrides/assets/favicon.ico
new file mode 100644
index 000000000000..a725c10e7251
Binary files /dev/null and b/docs/overrides/assets/favicon.ico differ
diff --git a/docs/overrides/assets/flame.svg b/docs/overrides/assets/flame.svg
new file mode 100644
index 000000000000..964782602e10
--- /dev/null
+++ b/docs/overrides/assets/flame.svg
@@ -0,0 +1 @@
+<svg role="img" width="250" aria-label="Visit CodeIgniter.com official website!" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 2100 500" height="60"><path fill="#ffffff" d="M148.2 411c-20.53-9.07-34.48-28.61-36.31-50.99 1.2-23.02 13.36-44.06 32.67-56.61-3.17 7.73-2.4 16.53 2 23.6 5.01 7 13.63 10.36 22.07 8.61 12.02-3.38 19.06-15.86 15.68-27.89-1.2-4.21-3.6-8.03-6.88-10.91-13.6-11.06-20.43-28.44-18-45.81 2.33-9.2 7.42-17.52 14.61-23.8-5.4 14.4 9.83 28.61 20.05 35.6 18.14 10.88 35.6 22.84 52.32 35.81 18.27 14.4 28.23 36.94 26.67 60-4.11 24.54-21.47 44.8-45.13 52.4 47.33-10.53 96.13-48.13 97.06-101.46-.93-42.67-26.4-80.96-65.33-98.4h-1.73c.86 2.09 1.28 4.34 1.2 6.61.13-1.47.13-2.93 0-4.4.21 1.73.21 3.47 0 5.2-2.96 12.13-15.2 19.6-27.36 16.64-4.86-1.2-9.2-3.93-12.32-7.87-15.6-20 0-42.76 2.61-64.76 1.6-28.13-11.25-55.02-34.05-71.46 11.41 19.02-3.79 44-14.84 58.21-11.07 14.21-27.07 24.8-40.11 37.2-14.05 13.07-26.93 27.44-38.49 42.8-24.99 30.53-34.8 70.8-26.67 109.4 11.15 37.2 42.07 65.15 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diff --git a/docs/overrides/assets/fonts/Inter/inter-latin-300-italic.woff2 b/docs/overrides/assets/fonts/Inter/inter-latin-300-italic.woff2
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diff --git a/docs/overrides/assets/fonts/Inter/inter-latin-400-italic.woff2 b/docs/overrides/assets/fonts/Inter/inter-latin-400-italic.woff2
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diff --git a/docs/overrides/assets/fonts/Inter/inter-latin-700-italic.woff2 b/docs/overrides/assets/fonts/Inter/inter-latin-700-italic.woff2
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diff --git a/docs/overrides/assets/fonts/JetBrainsMono/jetbrains-mono-latin-400-italic.woff2 b/docs/overrides/assets/fonts/JetBrainsMono/jetbrains-mono-latin-400-italic.woff2
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diff --git a/docs/overrides/assets/fonts/JetBrainsMono/jetbrains-mono-latin-700-italic.woff2 b/docs/overrides/assets/fonts/JetBrainsMono/jetbrains-mono-latin-700-italic.woff2
new file mode 100644
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diff --git a/docs/overrides/assets/fonts/JetBrainsMono/jetbrains-mono-latin-700-normal.woff2 b/docs/overrides/assets/fonts/JetBrainsMono/jetbrains-mono-latin-700-normal.woff2
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index 000000000000..3a4e333fc931
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diff --git a/docs/overrides/assets/js/code.js b/docs/overrides/assets/js/code.js
new file mode 100644
index 000000000000..6c61d334fb72
--- /dev/null
+++ b/docs/overrides/assets/js/code.js
@@ -0,0 +1,38 @@
+/* Splits Pygments' single keyword class the way VS Code's Modern themes do:
+   control-flow keywords and $this get their own classes for code.css to color. */
+const controlKeywords = new Set([
+    'if', 'else', 'elseif', 'switch', 'case', 'default', 'for', 'foreach',
+    'while', 'do', 'break', 'continue', 'return', 'try', 'catch', 'finally',
+    'throw', 'match', 'yield', 'goto',
+]);
+
+// Material's document$ emits on the first load and after every instant navigation.
+document$.subscribe(() => {
+    for (const span of document.querySelectorAll('.highlight .k')) {
+        if (controlKeywords.has(span.textContent)) {
+            span.classList.add('k-control');
+        }
+    }
+
+    for (const span of document.querySelectorAll('.highlight .nv')) {
+        if (span.textContent === '$this') {
+            span.classList.add('nv-this');
+        }
+    }
+
+    for (const span of document.querySelectorAll('.highlight .nx')) {
+        if (/^[A-Z][A-Z0-9_]*$/.test(span.textContent)) {
+            span.classList.add('nx-constant');
+        } else if (/^[A-Z]/.test(span.textContent)) {
+            span.classList.add('nx-class');
+        }
+    }
+
+    for (const span of document.querySelectorAll('.highlight .na')) {
+        const next = span.nextElementSibling;
+
+        if (next !== null && next.classList.contains('p') && next.textContent.startsWith('(')) {
+            span.classList.add('na-call');
+        }
+    }
+});
diff --git a/docs/overrides/assets/js/shortcuts.js b/docs/overrides/assets/js/shortcuts.js
new file mode 100644
index 000000000000..8d17b9a5170b
--- /dev/null
+++ b/docs/overrides/assets/js/shortcuts.js
@@ -0,0 +1,17 @@
+const isMac = /Mac|iPhone|iPad/.test(navigator.userAgentData?.platform ?? navigator.platform);
+
+document.querySelector('.md-search__form')?.setAttribute('data-shortcut', isMac ? '⌘K' : 'Ctrl K');
+
+document.addEventListener('keydown', (event) => {
+    if (event.key.toLowerCase() !== 'k' || !(isMac ? event.metaKey : event.ctrlKey)) {
+        return;
+    }
+
+    event.preventDefault();
+
+    const toggle = document.querySelector('[data-md-toggle="search"]');
+
+    toggle.checked = true;
+    toggle.dispatchEvent(new CustomEvent('change'));
+    document.querySelector('.md-search__input')?.focus();
+});
diff --git a/docs/overrides/assets/js/sidebar.js b/docs/overrides/assets/js/sidebar.js
new file mode 100644
index 000000000000..90d99a6efa59
--- /dev/null
+++ b/docs/overrides/assets/js/sidebar.js
@@ -0,0 +1,24 @@
+const navigationWrap = '.md-sidebar--primary .md-sidebar__scrollwrap';
+const navigationScrollKey = 'navigation.scroll';
+const scrollElementTo = Element.prototype.scrollTo;
+
+// The theme centers the active link on every page load, with no option to turn that off.
+Element.prototype.scrollTo = function (...position) {
+    const saved = this.matches(navigationWrap) ? __md_get(navigationScrollKey, sessionStorage) : null;
+    const active = saved === null ? null : this.querySelector('.md-nav__link--active[href]');
+
+    if (active === null) {
+        return scrollElementTo.apply(this, position);
+    }
+
+    const activeTop = active.getBoundingClientRect().top - this.getBoundingClientRect().top + this.scrollTop;
+    const isVisible = activeTop >= saved && activeTop + active.offsetHeight <= saved + this.clientHeight;
+
+    return isVisible ? scrollElementTo.call(this, { top: saved }) : scrollElementTo.apply(this, position);
+};
+
+document.addEventListener('scroll', (event) => {
+    if (event.target.matches?.(navigationWrap)) {
+        __md_set(navigationScrollKey, event.target.scrollTop, sessionStorage);
+    }
+}, { capture: true, passive: true });
diff --git a/docs/overrides/assets/js/versions.js b/docs/overrides/assets/js/versions.js
new file mode 100644
index 000000000000..8936b5e39b60
--- /dev/null
+++ b/docs/overrides/assets/js/versions.js
@@ -0,0 +1,129 @@
+const root = new URL(JSON.parse(document.querySelector('#__config').textContent).base, location).href;
+const isLocal = ['localhost', '127.0.0.1', ''].includes(location.hostname);
+const versionsUrl = isLocal ? new URL('assets/versions.json', root) : 'https://codeigniter4.github.io/CodeIgniter4/versions.json';
+
+const releaseUrl = 'https://api.github.com/repos/codeigniter4/CodeIgniter4/releases/latest';
+const releaseKey = 'version.latest';
+
+const latestTag = async () => {
+    try {
+        const cached = sessionStorage.getItem(releaseKey);
+
+        if (cached !== null) {
+            return cached;
+        }
+    } catch {}
+
+    const response = await fetch(releaseUrl);
+
+    if (!response.ok) {
+        throw new Error(response.status);
+    }
+
+    const { tag_name: tag } = await response.json();
+
+    try {
+        sessionStorage.setItem(releaseKey, tag);
+    } catch {}
+
+    return tag;
+};
+
+const withLatestTag = async (versions) => {
+    if (!versions.some((version) => version.title.includes('{tag}'))) {
+        return versions;
+    }
+
+    const tag = await latestTag().catch(() => null);
+
+    return versions.map((version) => ({
+        ...version,
+        title: tag === null ? version.title.replace(' ({tag})', '') : version.title.replace('{tag}', tag),
+    }));
+};
+
+const samePageIn =(version) => version.url + location.pathname.slice(new URL(root).pathname.length) + location.hash;
+
+const goTo = async (version) => {
+    const target = samePageIn(version);
+
+    try {
+        const response = await fetch(target, { method: 'HEAD' });
+
+        location.assign(response.status === 404 ? version.url : target);
+    } catch {
+        // A host without CORS headers hides the status, so the page is assumed to exist.
+        location.assign(target);
+    }
+};
+
+const renderVersions = (deployed) => {
+    const local = { title: 'Local build', url: root };
+    const current = deployed.find((version) => root === version.url) ?? local;
+    const versions = current === local ? [local, ...deployed] : deployed;
+    const selector = document.createElement('div');
+    const button = document.createElement('button');
+    const list = document.createElement('ul');
+
+    selector.className = 'md-version';
+    button.className = 'md-version__current';
+    button.setAttribute('aria-label', 'Select version');
+    button.setAttribute('aria-expanded', 'false');
+    button.textContent = current.title;
+    list.className = 'md-version__list';
+
+    const setOpen = (open) => {
+        selector.classList.toggle('md-version--open', open);
+        button.setAttribute('aria-expanded', String(open));
+    };
+
+    button.addEventListener('click', () => setOpen(!selector.classList.contains('md-version--open')));
+    document.addEventListener('click', (event) => {
+        if (!selector.contains(event.target)) {
+            setOpen(false);
+        }
+    });
+    document.addEventListener('keydown', (event) => {
+        if (event.key === 'Escape') {
+            setOpen(false);
+        }
+    });
+
+    const links = versions.map((version) => {
+        const item = document.createElement('li');
+        const link = document.createElement('a');
+
+        item.className = 'md-version__item';
+        link.className = 'md-version__link';
+        link.textContent = version.title;
+        link.addEventListener('click', (event) => {
+            if (event.metaKey || event.ctrlKey || event.shiftKey) {
+                return;
+            }
+
+            event.preventDefault();
+            event.stopPropagation();
+            goTo(version);
+        });
+
+        item.append(link);
+        list.append(item);
+
+        return [link, version];
+    });
+
+    selector.append(button, list);
+    document.querySelector('.md-header__title').after(selector);
+
+    document$.subscribe(() => {
+        links.forEach(([link, version]) => {
+            link.href = samePageIn(version);
+        });
+    });
+};
+
+fetch(versionsUrl)
+    .then((response) => (response.ok ? response.json() : Promise.reject(response.status)))
+    .then(withLatestTag)
+    .then(renderVersions)
+    .catch(() => {});
diff --git a/docs/overrides/assets/js/year.js b/docs/overrides/assets/js/year.js
new file mode 100644
index 000000000000..aa79e11111b1
--- /dev/null
+++ b/docs/overrides/assets/js/year.js
@@ -0,0 +1,3 @@
+document.querySelectorAll('[data-current-year]').forEach((element) => {
+    element.textContent = new Date().getFullYear();
+});
diff --git a/docs/overrides/assets/versions.json b/docs/overrides/assets/versions.json
new file mode 100644
index 000000000000..f7d2d103dbe5
--- /dev/null
+++ b/docs/overrides/assets/versions.json
@@ -0,0 +1,5 @@
+[
+    {"title": "Stable ({tag})", "url": "https://codeigniter.com/user_guide/"},
+    {"title": "Latest (develop)", "url": "https://codeigniter4.github.io/CodeIgniter4/develop/"},
+    {"title": "Next minor (4.8)", "url": "https://codeigniter4.github.io/CodeIgniter4/next/"}
+]
diff --git a/docs/overrides/partials/actions.html b/docs/overrides/partials/actions.html
new file mode 100644
index 000000000000..2e15c408ac3e
--- /dev/null
+++ b/docs/overrides/partials/actions.html
@@ -0,0 +1,21 @@
+{# Material's edit button, with the "Edit this page" label shown next to its icon. #}
+{% if page.edit_url %}
+  {% if "content.action.edit" in features %}
+    <a href="{{ page.edit_url }}" title="{{ lang.t('action.edit') }}" class="md-content__button md-content__button--labelled md-icon" rel="edit">
+      {% set icon = config.theme.icon.edit or "material/file-edit-outline" %}
+      {% include ".icons/" ~ icon ~ ".svg" %}
+      <span>{{ lang.t('action.edit') }}</span>
+    </a>
+  {% endif %}
+  {% if "content.action.view" in features %}
+    {% if "/blob/" in page.edit_url %}
+      {% set part = "blob" %}
+    {% else %}
+      {% set part = "edit" %}
+    {% endif %}
+    <a href="{{ page.edit_url | replace(part, 'raw') }}" title="{{ lang.t('action.view') }}" class="md-content__button md-icon">
+      {% set icon = config.theme.icon.view or "material/file-eye-outline" %}
+      {% include ".icons/" ~ icon ~ ".svg" %}
+    </a>
+  {% endif %}
+{% endif %}
diff --git a/docs/requirements.txt b/docs/requirements.txt
new file mode 100644
index 000000000000..b5a84edda6cd
--- /dev/null
+++ b/docs/requirements.txt
@@ -0,0 +1,2 @@
+mkdocs-material==9.8.0
+pygments==2.21.0
diff --git a/mkdocs.yml b/mkdocs.yml
new file mode 100644
index 000000000000..cc73418bb32b
--- /dev/null
+++ b/mkdocs.yml
@@ -0,0 +1,105 @@
+# The nav is docs/.nav.yml, kept up to date by admin/update-docs-nav.php.
+INHERIT: docs/.nav.yml
+
+site_name: CodeIgniter
+site_description: Main user guide for the CodeIgniter 4 framework
+# Set per deployment, since instant navigation and the sitemap need the site's own URL.
+site_url: !ENV SITE_URL
+use_directory_urls: false
+
+# Files in docs/ that are not pages.
+exclude_docs: |
+  overrides/
+  requirements.txt
+
+theme:
+  name: material
+  custom_dir: docs/overrides
+  logo: assets/flame.svg
+  favicon: assets/favicon.ico
+  font: false
+  icon:
+    repo: fontawesome/brands/github
+  palette:
+    - media: "(prefers-color-scheme: light)"
+      scheme: codeigniter
+      primary: custom
+      accent: custom
+      toggle:
+        icon: material/brightness-7
+        name: Switch to dark mode
+    - media: "(prefers-color-scheme: dark)"
+      scheme: slate
+      primary: custom
+      accent: custom
+      toggle:
+        icon: material/brightness-4
+        name: Switch to light mode
+  features:
+    - navigation.instant
+    - navigation.instant.prefetch
+    - navigation.instant.progress
+    - content.code.copy
+    - navigation.footer
+    - content.action.edit
+    - navigation.top
+    - search.suggest
+    - search.highlight
+    - search.share
+    - navigation.path
+    - toc.follow
+
+extra:
+  homepage: https://codeigniter.com
+  generator: false
+
+  social:
+    - icon: material/github
+      link: https://github.com/codeigniter4/CodeIgniter4
+      name: GitHub
+    - icon: material/twitter
+      link: https://twitter.com/CodeIgniterPhp
+      name: X
+    - icon: material/forum
+      link: https://forum.codeigniter.com
+      name: Forum Codeigniter
+    - icon: material/slack
+      link: https://join.slack.com/t/codeigniterchat/shared_invite/zt-244xrrslc-l_I69AJSi5y2a2RVN~xIdQ
+      name: Slack
+
+repo_name: codeigniter4/CodeIgniter4
+repo_url: https://github.com/codeigniter4/CodeIgniter4
+edit_uri: edit/develop/docs/
+copyright: Copyright &copy; 2019-<span data-current-year>2026</span> CodeIgniter Foundation.
+
+validation:
+  anchors: warn
+
+markdown_extensions:
+  - admonition
+  - pymdownx.superfences
+  - pymdownx.highlight:
+      extend_pygments_lang:
+        # PHP samples have no opening tag.
+        - name: php
+          lang: php
+          options:
+            startinline: true
+  - toc:
+      permalink: true
+      toc_depth: 3
+  - tables
+
+extra_css:
+  - assets/css/fonts.css
+  - assets/css/codeigniter.css
+  - assets/css/codeigniter_dark_mode.css
+  - assets/css/layout.css
+  - assets/css/code.css
+
+extra_javascript:
+  - assets/js/shortcuts.js
+  - assets/js/code.js
+  - assets/js/versions.js
+  - assets/js/sidebar.js
+  - assets/js/year.js
diff --git a/tests/system/AutoReview/UpdateDocsNavTest.php b/tests/system/AutoReview/UpdateDocsNavTest.php
new file mode 100644
index 000000000000..837604ee8193
--- /dev/null
+++ b/tests/system/AutoReview/UpdateDocsNavTest.php
@@ -0,0 +1,181 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of CodeIgniter 4 framework.
+ *
+ * (c) CodeIgniter Foundation <admin@codeigniter.com>
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace CodeIgniter\AutoReview;
+
+use FilesystemIterator;
+use PHPUnit\Framework\Attributes\CoversNothing;
+use PHPUnit\Framework\Attributes\Group;
+use PHPUnit\Framework\TestCase;
+use RecursiveDirectoryIterator;
+use RecursiveIteratorIterator;
+
+/**
+ * @internal
+ */
+#[CoversNothing]
+#[Group('AutoReview')]
+final class UpdateDocsNavTest extends TestCase
+{
+    private const NAV = <<<'YAML'
+        nav:
+          - Home: index.md
+          - "Installation":
+              - installation/index.md
+              - "Change Logs":
+                  - changelogs/index.md
+                  - changelogs/v1.2.0.md
+                  - changelogs/v1.0.0.md
+              - "Upgrading":
+                  - installation/upgrading.md
+                  - installation/upgrade_100.md
+        YAML;
+
+    private string $docs;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->docs = sys_get_temp_dir() . '/docs-nav-' . bin2hex(random_bytes(4));
+
+        $this->write('.nav.yml', self::NAV . "\n");
+        $this->write('index.md', "# Home\n");
+        $this->write('installation/index.md', "- [v1.2.0](../changelogs/v1.2.0.md)\n- [Upgrade](upgrade_100.md)\n");
+        $this->write('changelogs/index.md', "- [v1.3.0](v1.3.0.md)\n- [v1.2.0](v1.2.0.md)\n- [v1.1.0](v1.1.0.md)\n- [v1.0.0](v1.0.0.md)\n");
+        $this->write('installation/upgrading.md', "- [Upgrade 1.0.0](upgrade_100.md)\n- [Upgrade 1.1.0](upgrade_110.md)\n");
+
+        foreach (['changelogs/v1.2.0.md', 'changelogs/v1.0.0.md', 'installation/upgrade_100.md'] as $page) {
+            $this->write($page, "# Page\n");
+        }
+    }
+
+    protected function tearDown(): void
+    {
+        $files = new RecursiveIteratorIterator(
+            new RecursiveDirectoryIterator($this->docs, FilesystemIterator::SKIP_DOTS),
+            RecursiveIteratorIterator::CHILD_FIRST,
+        );
+
+        foreach ($files as $file) {
+            $file->isDir() ? rmdir($file->getPathname()) : unlink($file->getPathname());
+        }
+
+        rmdir($this->docs);
+
+        parent::tearDown();
+    }
+
+    public function testErrorWhenNavIsMissing(): void
+    {
+        unlink($this->docs . '/.nav.yml');
+
+        $result = $this->runScript('');
+
+        $this->assertSame(1, $result['exitCode']);
+        $this->assertStringContainsString('is not found', $result['output']);
+    }
+
+    public function testCheckPassesWhenNavIsComplete(): void
+    {
+        $this->write('changelogs/v1.3.0.md', "# Page\n");
+        $this->write('changelogs/v1.1.0.md', "# Page\n");
+        $this->write('installation/upgrade_110.md', "# Page\n");
+        $this->write('.nav.yml', str_replace(
+            "          - changelogs/v1.2.0.md\n          - changelogs/v1.0.0.md\n",
+            "          - changelogs/v1.3.0.md\n          - changelogs/v1.2.0.md\n          - changelogs/v1.1.0.md\n          - changelogs/v1.0.0.md\n",
+            self::NAV . "\n          - installation/upgrade_110.md\n",
+        ));
+
+        $result = $this->runScript('--check');
+
+        $this->assertSame(0, $result['exitCode']);
+        $this->assertSame('', $result['output']);
+    }
+
+    public function testCheckReportsMissingAndStalePagesWithoutChangingTheNav(): void
+    {
+        $this->write('changelogs/v1.3.0.md', "# Page\n");
+        unlink($this->docs . '/installation/upgrade_100.md');
+
+        $result = $this->runScript('--check');
+
+        $this->assertSame(1, $result['exitCode']);
+        $this->assertStringContainsString('changelogs/v1.3.0.md is missing from the nav', $result['output']);
+        $this->assertStringContainsString('The nav lists installation/upgrade_100.md, which does not exist', $result['output']);
+        $this->assertSame(self::NAV . "\n", file_get_contents($this->docs . '/.nav.yml'));
+    }
+
+    public function testMissingPagesAreInsertedInTheOrderOfTheSectionIndex(): void
+    {
+        $this->write('changelogs/v1.3.0.md', "# Page\n");
+        $this->write('changelogs/v1.1.0.md', "# Page\n");
+        $this->write('installation/upgrade_110.md', "# Page\n");
+
+        $result = $this->runScript('');
+
+        $this->assertSame(0, $result['exitCode']);
+        $this->assertSame(
+            <<<'YAML'
+                nav:
+                  - Home: index.md
+                  - "Installation":
+                      - installation/index.md
+                      - "Change Logs":
+                          - changelogs/index.md
+                          - changelogs/v1.3.0.md
+                          - changelogs/v1.2.0.md
+                          - changelogs/v1.1.0.md
+                          - changelogs/v1.0.0.md
+                      - "Upgrading":
+                          - installation/upgrading.md
+                          - installation/upgrade_100.md
+                          - installation/upgrade_110.md
+
+                YAML,
+            file_get_contents($this->docs . '/.nav.yml'),
+        );
+    }
+
+    public function testPageThatNoSectionLinksToIsAddedAtTheEnd(): void
+    {
+        $this->write('extra.md', "# Page\n");
+
+        $result = $this->runScript('');
+
+        $this->assertSame(0, $result['exitCode']);
+        $this->assertStringContainsString('Move it by hand', $result['output']);
+        $this->assertStringEndsWith("  - extra.md\n", (string) file_get_contents($this->docs . '/.nav.yml'));
+    }
+
+    /**
+     * @return array{exitCode: int, output: string}
+     */
+    private function runScript(string $options): array
+    {
+        exec(sprintf('php ./admin/update-docs-nav.php %s --docs=%s 2>&1', $options, escapeshellarg($this->docs)), $output, $exitCode);
+
+        return ['exitCode' => $exitCode, 'output' => implode("\n", $output)];
+    }
+
+    private function write(string $path, string $contents): void
+    {
+        $file = $this->docs . '/' . $path;
+
+        if (! is_dir(dirname($file))) {
+            mkdir(dirname($file), 0777, true);
+        }
+
+        file_put_contents($file, $contents);
+    }
+}