diff --git a/frontend/css/main.css b/frontend/css/main.css
index b9811dc..3d573e0 100644
--- a/frontend/css/main.css
+++ b/frontend/css/main.css
@@ -201,6 +201,7 @@ input[type="radio"]:checked + label .neon-indicator { display: block; }
 
 /* ── Semantic border utility classes ── */
 .border-b-medium { border-bottom: 1px solid rgba(255,255,255,0.08); }
+.border-t-medium { border-top:    1px solid rgba(255,255,255,0.08); }
 
 /* ── Search container ── */
 .search-container {
@@ -375,3 +376,213 @@ input[type="radio"]:checked + label .neon-indicator { display: block; }
 .htmx-indicator { display: none; }
 .htmx-request .htmx-indicator { display: flex; }
 .htmx-request.htmx-indicator { display: flex; }
+
+/* ── Theme toggle button ── */
+.btn-icon-theme {
+    display: flex; align-items: center; justify-content: center;
+    width: 34px; height: 34px; border-radius: 8px;
+    color: var(--color-text-muted);
+    background: transparent; border: none;
+    transition: color 0.15s, background 0.15s;
+}
+.btn-icon-theme:hover {
+    color: var(--color-text-body);
+    background: rgba(255,255,255,0.07);
+}
+
+/* ── Theme toggle icon visibility ── */
+.theme-moon { display: none; }
+[data-theme="light"] .theme-sun { display: none; }
+[data-theme="light"] .theme-moon { display: block; }
+
+/* ══════════════════════════════════════════════
+   LIGHT THEME
+   ══════════════════════════════════════════════ */
+
+[data-theme="light"] {
+    --color-text-bright: #0e1018;
+    --color-text-active: #181c28;
+    --color-text-body:   #2e3650;
+    --color-text-muted:  #606880;
+    --color-text-subtle: #98a0b4;
+    --color-bg-base:     #f0f2f8;
+    --color-bg-card:     #ffffff;
+}
+
+[data-theme="light"] select { color-scheme: light; }
+
+[data-theme="light"] ::selection {
+    background: rgba(0,229,255,0.25); color: #0e1018;
+}
+[data-theme="light"] ::-webkit-scrollbar-thumb {
+    background: rgba(0,0,0,0.14);
+}
+
+/* Light mode neon grid — tone down blobs, remove scanlines */
+[data-theme="light"] .neon-blob-1 { background: radial-gradient(ellipse, rgba(255,45,123,0.05), transparent 70%); }
+[data-theme="light"] .neon-blob-2 { background: radial-gradient(ellipse, rgba(0,229,255,0.04), transparent 65%); }
+[data-theme="light"] .neon-blob-3 { background: radial-gradient(ellipse, rgba(180,77,255,0.03), transparent 60%); }
+[data-theme="light"] .neon-blob-4 { background: radial-gradient(ellipse, rgba(255,215,0,0.02), transparent 55%); }
+[data-theme="light"] .neon-scanlines { display: none; }
+
+/* Light mode glass containers */
+[data-theme="light"] .glass-outer {
+    background: rgba(255,255,255,0.80);
+    border-color: rgba(0,0,0,0.09);
+    box-shadow: 0 8px 40px rgba(0,0,0,0.07);
+}
+[data-theme="light"] .glass-inner {
+    background: rgba(0,0,0,0.04);
+    border-color: rgba(0,0,0,0.14);
+}
+[data-theme="light"] .glass-inset {
+    background: rgba(0,0,0,0.05);
+    border-color: rgba(0,0,0,0.16);
+}
+[data-theme="light"] .glass-inset:hover {
+    background: rgba(0,0,0,0.09);
+    border-color: rgba(0,0,0,0.22);
+}
+
+/* Light mode nav */
+[data-theme="light"] .nav-active { background: rgba(0,0,0,0.08); }
+[data-theme="light"] .nav-link-active { background: rgba(0,0,0,0.08); }
+[data-theme="light"] .btn-icon-theme:hover { background: rgba(0,0,0,0.08); }
+
+/* Light mode header / footer */
+[data-theme="light"] .site-header {
+    background: rgba(240,242,248,0.92);
+    border-bottom-color: rgba(0,0,0,0.14);
+}
+[data-theme="light"] .site-footer {
+    background: rgba(240,242,248,0.92);
+    border-top-color: rgba(0,0,0,0.14);
+}
+
+/* Light mode mobile menu nav drawer */
+[data-theme="light"] #mobile-menu nav {
+    background: rgba(242,244,250,0.98);
+}
+[data-theme="light"] #mobile-menu nav > div:last-child {
+    border-top-color: rgba(0,0,0,0.14);
+}
+[data-theme="light"] #mobile-menu button:hover,
+[data-theme="light"] #mobile-menu a:hover {
+    background: rgba(0,0,0,0.08) !important;
+}
+
+/* Light mode search */
+[data-theme="light"] .search-container {
+    background: rgba(255,255,255,0.92);
+    border-color: rgba(0,0,0,0.16);
+    box-shadow: 0 8px 40px rgba(0,0,0,0.07);
+}
+[data-theme="light"] .search-container:focus-within {
+    border-color: rgba(0,150,200,0.55);
+    box-shadow: 0 0 0 5px rgba(0,150,200,0.08), 0 8px 40px rgba(0,0,0,0.09);
+}
+
+/* Light mode cards / toggles */
+[data-theme="light"] .source-toggle {
+    background: rgba(0,0,0,0.05);
+    border-color: rgba(0,0,0,0.16);
+}
+[data-theme="light"] .recent-search-card {
+    background: rgba(0,0,0,0.05);
+    border-color: rgba(0,0,0,0.16);
+}
+[data-theme="light"] .recent-search-card:hover {
+    background: rgba(0,0,0,0.09);
+    border-color: rgba(0,0,0,0.22);
+}
+[data-theme="light"] .data-source-card {
+    background: rgba(0,0,0,0.05);
+    border-color: rgba(0,0,0,0.16);
+}
+[data-theme="light"] .data-source-card:hover {
+    background: rgba(0,0,0,0.09);
+    border-color: rgba(0,0,0,0.22);
+}
+
+/* Light mode buttons — use solid tones so they're clearly visible */
+[data-theme="light"] .btn-ghost {
+    background: #e6e8ef;
+    border-color: #bfc2cc;
+}
+[data-theme="light"] .btn-ghost:hover {
+    background: #d8dbe5;
+    border-color: #b0b3be;
+}
+
+/* Light mode dividers / progress */
+[data-theme="light"] .border-b-medium { border-bottom-color: rgba(0,0,0,0.14); }
+[data-theme="light"] .border-t-medium { border-top-color:    rgba(0,0,0,0.14); }
+[data-theme="light"] .neon-progress { background: rgba(0,0,0,0.12); }
+
+/* Light mode docs */
+[data-theme="light"] .docs-code {
+    background: #e8eaf0;
+    border-color: rgba(0,0,0,0.14);
+}
+[data-theme="light"] .docs-toc-link:hover { background: rgba(0,0,0,0.07); }
+[data-theme="light"] .docs-table th { border-bottom-color: rgba(0,0,0,0.16); }
+[data-theme="light"] .docs-table td { border-bottom-color: rgba(0,0,0,0.10); }
+
+/* ── Light mode: flip Tailwind white-overlay utilities → dark-overlay ── */
+/*
+ * rgba(0,0,0,X) on bg #f0f2f8 produces:
+ *  0.07 → #dfe1e6  0.10 → #d8d9df  0.14 → #cfd1d7  0.20 → #c4c6cb
+ * Borders need ≥0.18 to be clearly visible; backgrounds ≥0.07 to read as a surface.
+ */
+
+/* Backgrounds */
+[data-theme="light"] .bg-white\/5,
+[data-theme="light"] .bg-white\/\[0\.05\] { background-color: rgba(0,0,0,0.07); }
+[data-theme="light"] .bg-white\/\[0\.03\] { background-color: rgba(0,0,0,0.05); }
+[data-theme="light"] .bg-white\/\[0\.04\] { background-color: rgba(0,0,0,0.06); }
+[data-theme="light"] .bg-white\/\[0\.06\] { background-color: rgba(0,0,0,0.08); }
+[data-theme="light"] .bg-white\/\[0\.08\] { background-color: rgba(0,0,0,0.09); }
+[data-theme="light"] .bg-white\/10      { background-color: rgba(0,0,0,0.11); }
+
+/* Hover backgrounds */
+[data-theme="light"] .hover\:bg-white\/5:hover      { background-color: rgba(0,0,0,0.09); }
+[data-theme="light"] .hover\:bg-white\/\[0\.02\]:hover { background-color: rgba(0,0,0,0.05); }
+[data-theme="light"] .hover\:bg-white\/\[0\.06\]:hover { background-color: rgba(0,0,0,0.09); }
+[data-theme="light"] .hover\:bg-white\/\[0\.08\]:hover { background-color: rgba(0,0,0,0.11); }
+[data-theme="light"] .hover\:bg-white\/10:hover     { background-color: rgba(0,0,0,0.13); }
+
+/* Borders */
+[data-theme="light"] .border-white\/\[0\.06\] { border-color: rgba(0,0,0,0.14); }
+[data-theme="light"] .border-white\/\[0\.08\] { border-color: rgba(0,0,0,0.16); }
+[data-theme="light"] .border-white\/10       { border-color: rgba(0,0,0,0.20); }
+[data-theme="light"] .border-white\/20       { border-color: rgba(0,0,0,0.28); }
+[data-theme="light"] .hover\:border-white\/\[0\.14\]:hover { border-color: rgba(0,0,0,0.22); }
+
+/* Ring (avatar images etc.) */
+[data-theme="light"] .ring-white\/10 { --tw-ring-color: rgba(0,0,0,0.10); }
+
+/* Search extension article — dark overlay card → white card */
+[data-theme="light"] article.rounded-xl { background-color: rgba(255,255,255,0.90); }
+
+/* ── Light mode: accessible text colors ── */
+/* neon-cyan (#00e5ff) is ~1.2:1 on white — replace with sky-600 (#0284c7 ~4.7:1) */
+[data-theme="light"] .text-neon-cyan { color: #0284c7; }
+
+/* neon-pink / brand (#ff2d7b) is ~3.6:1 — replace with pink-700 (#be185d ~5.0:1) */
+[data-theme="light"] .text-neon-pink,
+[data-theme="light"] .hover\:text-neon-pink:hover,
+[data-theme="light"] .text-brand-400,
+[data-theme="light"] .text-brand-500,
+[data-theme="light"] .text-brand-600 { color: #be185d; }
+[data-theme="light"] .text-brand-700,
+[data-theme="light"] .hover\:text-brand-700:hover { color: #9d174d; } /* pink-800 ~6.9:1 */
+
+/* Pastel status colors fail on light backgrounds: */
+[data-theme="light"] .text-green-400 { color: #16a34a; } /* green-600  ~5.1:1 */
+[data-theme="light"] .text-amber-400 { color: #b45309; } /* amber-700  ~5.4:1 */
+[data-theme="light"] .text-red-400   { color: #dc2626; } /* red-600    ~5.9:1 */
+
+/* Adjust badge backgrounds to match the darker text colors */
+[data-theme="light"] .bg-green-500\/10 { background-color: rgba(22,163,74,0.08); }
+[data-theme="light"] .bg-amber-500\/10 { background-color: rgba(180,83,9,0.08); }
+[data-theme="light"] .bg-red-500\/10   { background-color: rgba(220,38,38,0.08); }
diff --git a/internal/ui/icon/theme.templ b/internal/ui/icon/theme.templ
index 39f4add..b6383ad 100644
--- a/internal/ui/icon/theme.templ
+++ b/internal/ui/icon/theme.templ
@@ -2,8 +2,24 @@ package icon
 
 import "strconv"
 
+// Theme is the WordPress/data-source theme icon (image/picture).
 templ Theme(size int) {
 	<svg width={ strconv.Itoa(size) } height={ strconv.Itoa(size) } viewBox="0 0 24 24" fill="currentColor" fill-rule="evenodd" clip-rule="evenodd" aria-hidden="true">
 		<path d="M16.375 4.5H4.625a.125.125 0 0 0-.125.125v8.254l2.859-1.54a.75.75 0 0 1 .68-.016l2.384 1.142 2.89-2.074a.75.75 0 0 1 .874 0l2.313 1.66V4.625a.125.125 0 0 0-.125-.125Zm.125 9.398-2.75-1.975-2.813 2.02a.75.75 0 0 1-.76.067l-2.444-1.17L4.5 14.583v1.792c0 .069.056.125.125.125h11.75a.125.125 0 0 0 .125-.125v-2.477ZM4.625 3C3.728 3 3 3.728 3 4.625v11.75C3 17.273 3.728 18 4.625 18h11.75c.898 0 1.625-.727 1.625-1.625V4.625C18 3.728 17.273 3 16.375 3H4.625ZM20 8v11c0 .69-.31 1-.999 1H6v1.5h13.001c1.52 0 2.499-.982 2.499-2.5V8H20Z"></path>
 	</svg>
 }
+
+// Sun icon — shown in dark mode (click to switch to light)
+templ Sun(size int) {
+	<svg width={ strconv.Itoa(size) } height={ strconv.Itoa(size) } viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+		<circle cx="12" cy="12" r="4"></circle>
+		<path d="M12 2v2M12 20v2M4.93 4.93l1.41 1.41M17.66 17.66l1.41 1.41M2 12h2M20 12h2M6.34 17.66l-1.41 1.41M19.07 4.93l-1.41 1.41"></path>
+	</svg>
+}
+
+// Moon icon — shown in light mode (click to switch to dark)
+templ Moon(size int) {
+	<svg width={ strconv.Itoa(size) } height={ strconv.Itoa(size) } viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+		<path d="M21 12.79A9 9 0 1 1 11.21 3 7 7 0 0 0 21 12.79z"></path>
+	</svg>
+}
diff --git a/internal/ui/layout/base.templ b/internal/ui/layout/base.templ
index e41d678..ade1b93 100644
--- a/internal/ui/layout/base.templ
+++ b/internal/ui/layout/base.templ
@@ -7,7 +7,7 @@ import (
 
 templ Base(pd ui.PageData) {
 	<!DOCTYPE html>
-	<html lang="en">
+	<html lang="en" data-theme="dark">
 	<head>
 		<meta charset="UTF-8"/>
 		<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
@@ -16,6 +16,7 @@ templ Base(pd ui.PageData) {
 		@Head(pd)
 		<link rel="icon" href="/favicon.svg" type="image/svg+xml"/>
 		<link rel="icon" href="/favicon.ico" sizes="32x32"/>
+		@themeInitScript()
 		<link rel="stylesheet" href={ "/static/css/styles.css?v=" + pd.Version }/>
 		<script src={ "/static/js/htmx.min.js?v=" + pd.Version }></script>
 	</head>
@@ -34,6 +35,7 @@ templ Base(pd ui.PageData) {
 		@nav.Footer(pd.Version, pd.RequestStart)
 		<div id="context-modal"></div>
 		@mobileMenuScript()
+		@themeToggleScript()
 	</body>
 	</html>
 }
@@ -48,6 +50,28 @@ templ neonGrid() {
 	</div>
 }
 
+// themeInitScript runs before CSS loads to avoid flash-of-wrong-theme.
+templ themeInitScript() {
+	<script>
+		(function() {
+			var t = localStorage.getItem('veloria-theme');
+			if (!t) t = window.matchMedia('(prefers-color-scheme: light)').matches ? 'light' : 'dark';
+			document.documentElement.dataset.theme = t;
+		})();
+	</script>
+}
+
+templ themeToggleScript() {
+	<script>
+		function toggleTheme() {
+			var html = document.documentElement;
+			var next = html.dataset.theme === 'light' ? 'dark' : 'light';
+			html.dataset.theme = next;
+			localStorage.setItem('veloria-theme', next);
+		}
+	</script>
+}
+
 templ mobileMenuScript() {
 	<script>
 		function toggleMobileMenu() {
diff --git a/internal/ui/nav/header.templ b/internal/ui/nav/header.templ
index b268d21..7e940e6 100644
--- a/internal/ui/nav/header.templ
+++ b/internal/ui/nav/header.templ
@@ -18,6 +18,10 @@ templ DesktopHeader(currentPath string, u *user.User) {
 						@DesktopNavLink(item)
 					}
 					<div class="w-px h-6 mx-2 bg-gradient-to-b from-transparent via-white/10 to-transparent"></div>
+					<button onclick="toggleTheme()" class="btn-icon-theme" aria-label="Toggle theme" hx-boost="false">
+						<span class="theme-sun">@icon.Sun(18)</span>
+						<span class="theme-moon">@icon.Moon(18)</span>
+					</button>
 					if u != nil {
 						@userSection(u)
 					} else {
diff --git a/internal/ui/nav/mobile_menu.templ b/internal/ui/nav/mobile_menu.templ
index f2a9eb8..df6c416 100644
--- a/internal/ui/nav/mobile_menu.templ
+++ b/internal/ui/nav/mobile_menu.templ
@@ -12,9 +12,15 @@ templ MobileHeader(currentPath string, u *user.User) {
 				@icon.Logo(28)
 				<span class="text-lg font-bold tracking-wide text-text-bright">Veloria</span>
 			</a>
-			<button type="button" onclick="toggleMobileMenu()" class="p-2 rounded-xl hover:bg-white/5 transition" aria-label="Open menu" aria-expanded="false" id="mobile-menu-button" hx-boost="false">
-				@icon.Menu(24)
-			</button>
+			<div class="flex items-center gap-1">
+				<button onclick="toggleTheme()" class="btn-icon-theme" aria-label="Toggle theme" hx-boost="false">
+					<span class="theme-sun">@icon.Sun(20)</span>
+					<span class="theme-moon">@icon.Moon(20)</span>
+				</button>
+				<button type="button" onclick="toggleMobileMenu()" class="p-2 rounded-xl hover:bg-white/5 transition" aria-label="Open menu" aria-expanded="false" id="mobile-menu-button" hx-boost="false">
+					@icon.Menu(24)
+				</button>
+			</div>
 		</div>
 	</header>
 	<!-- Mobile Menu Overlay -->
diff --git a/internal/ui/page/extension.templ b/internal/ui/page/extension.templ
index 6dd79c7..0808664 100644
--- a/internal/ui/page/extension.templ
+++ b/internal/ui/page/extension.templ
@@ -186,7 +186,7 @@ templ Extension(data ui.ExtensionData) {
 		if data.Indexed && len(data.LargestFiles) > 0 {
 			<!-- Largest Files -->
 			<div class="glass-inner overflow-hidden mb-6">
-				<div class="px-6 py-4" style="border-bottom: 1px solid rgba(255,255,255,0.08);">
+				<div class="px-6 py-4 border-b-medium">
 					<h2 class="text-xl font-semibold text-text-bright">Largest Files</h2>
 					<p class="text-sm text-text-muted">Top { strconv.Itoa(len(data.LargestFiles)) } by size</p>
 				</div>
diff --git a/internal/ui/partial/datasource_items.templ b/internal/ui/partial/datasource_items.templ
index e99889d..58d47db 100644
--- a/internal/ui/partial/datasource_items.templ
+++ b/internal/ui/partial/datasource_items.templ
@@ -20,7 +20,7 @@ templ DataSourceItems(data ui.DataSourceItemsData) {
 	if len(data.Items) > 0 {
 		<div>
 			for _, item := range data.Items {
-				<a href={ templ.SafeURL("/data-sources/" + data.DataSource + "/" + item.Slug) } class="px-6 py-4 flex items-center justify-between hover:bg-white/[0.08] transition-colors block" style="border-bottom: 1px solid rgba(255,255,255,0.06);">
+				<a href={ templ.SafeURL("/data-sources/" + data.DataSource + "/" + item.Slug) } class="px-6 py-4 flex items-center justify-between hover:bg-white/[0.08] transition-colors block border-b-medium">
 					<div class="flex items-center gap-4">
 						<div>
 							<h3 class="text-text-bright font-medium">{ item.Name }</h3>
@@ -42,7 +42,7 @@ templ DataSourceItems(data ui.DataSourceItemsData) {
 		</div>
 		<!-- Pagination -->
 		if data.TotalPages > 1 {
-			<div class="px-6 py-4 flex items-center justify-between" style="border-top: 1px solid rgba(255,255,255,0.08);">
+			<div class="px-6 py-4 flex items-center justify-between border-t-medium">
 				<p class="text-sm text-text-muted">
 					{ fmt.Sprintf("Page %d of %d", data.Page, data.TotalPages) }
 				</p>