diff --git a/frontend/src/App.vue b/frontend/src/App.vue
index 4b9a00b..37ee01d 100644
--- a/frontend/src/App.vue
+++ b/frontend/src/App.vue
@@ -44,9 +44,20 @@
 
                     <!-- Search -->
                     <div class="search-box nav-search" v-if="!isAdminRoute">
-                        <input type="text" class="form-control form-control-sm" placeholder="Search notes..." v-model="searchQuery" @keyup.enter="performSearch" />
+                        <input type="text" class="form-control" placeholder="Search notes..." v-model="searchQuery" @keyup.enter="performSearch" />
                     </div>
 
+                    <!-- Theme Toggle -->
+                    <button
+                        class="btn btn-outline-light theme-toggle"
+                        type="button"
+                        :aria-label="isDarkMode ? 'Switch to light mode' : 'Switch to dark mode'"
+                        :title="isDarkMode ? 'Switch to light mode' : 'Switch to dark mode'"
+                        @click="isDarkMode = !isDarkMode"
+                    >
+                        <i :class="isDarkMode ? 'mdi mdi-weather-sunny' : 'mdi mdi-weather-night'" aria-hidden="true"></i>
+                    </button>
+
                     <!-- User Menu -->
                     <div ref="userDropdownRef" class="dropdown nav-user-menu" v-if="currentUser" @mouseleave="showUserMenu = false">
                         <button class="btn btn-outline-light dropdown-toggle" type="button" @click="toggleUserMenu">
@@ -322,6 +333,13 @@ const shareCopied = ref(false);
 const shareCopyTimeout = ref(null);
 const noteViewMode = ref(localStorage.getItem("noteViewMode") || "grid");
 watch(noteViewMode, (val) => localStorage.setItem("noteViewMode", val));
+const isDarkMode = ref(localStorage.getItem("theme") === "dark");
+const applyTheme = (dark) => {
+    document.documentElement.setAttribute("data-bs-theme", dark ? "dark" : "light");
+    localStorage.setItem("theme", dark ? "dark" : "light");
+};
+watch(isDarkMode, applyTheme);
+applyTheme(isDarkMode.value);
 const showUnlockModal = ref(false);
 const unlockTargetNote = ref(null);
 const unlockPassword = ref("");
@@ -1191,4 +1209,21 @@ const logout = () => {
         width: 100%;
     }
 }
+
+/* Dark mode overrides */
+:root[data-bs-theme="dark"] .sidebar-header {
+    border-bottom-color: #3a3f4b;
+}
+
+:root[data-bs-theme="dark"] .breadcrumb-title {
+    color: #94a3b8;
+}
+
+:root[data-bs-theme="dark"] .breadcrumb-link {
+    color: #7aa2f7;
+}
+
+:root[data-bs-theme="dark"] .breadcrumb-separator {
+    color: #4a5568;
+}
 </style>
diff --git a/frontend/src/assets/styles/main.css b/frontend/src/assets/styles/main.css
index 311c81e..a937a5f 100644
--- a/frontend/src/assets/styles/main.css
+++ b/frontend/src/assets/styles/main.css
@@ -6,6 +6,75 @@
     --border-color: #dee2e6;
 }
 
+[data-bs-theme="dark"] {
+    --text-color: #e2e8f0;
+    --bg-color: #1a1d23;
+    --border-color: #3a3f4b;
+}
+
+[data-bs-theme="dark"] body {
+    background-color: #1a1d23;
+    color: #e2e8f0;
+}
+
+[data-bs-theme="dark"] .sidebar {
+    background-color: #21252e !important;
+    border-color: #3a3f4b !important;
+}
+
+[data-bs-theme="dark"] .toolbar {
+    background-color: #21252e;
+    border-color: #3a3f4b !important;
+}
+
+[data-bs-theme="dark"] .main-content {
+    background-color: #1a1d23;
+}
+
+[data-bs-theme="dark"] .markdown-body table {
+    background: #21252e;
+}
+
+[data-bs-theme="dark"] .markdown-body th {
+    background: #2a2f3a;
+}
+
+[data-bs-theme="dark"] .markdown-body tr:nth-child(even) td {
+    background: #232830;
+}
+
+[data-bs-theme="dark"] .markdown-body blockquote {
+    background: #1e2430;
+    color: #a0aec0;
+}
+
+[data-bs-theme="dark"] .markdown-body :not(pre) > code {
+    background: #2d3748;
+    color: #e2e8f0;
+}
+
+[data-bs-theme="dark"] .markdown-body pre code {
+    background: transparent;
+    color: inherit;
+}
+
+[data-bs-theme="dark"] .markdown-body pre {
+    background: #2d3748;
+    color: #e2e8f0;
+}
+
+[data-bs-theme="dark"] ::-webkit-scrollbar-track {
+    background: #2d3748;
+}
+
+[data-bs-theme="dark"] ::-webkit-scrollbar-thumb {
+    background: #4a5568;
+}
+
+[data-bs-theme="dark"] ::-webkit-scrollbar-thumb:hover {
+    background: #718096;
+}
+
 * {
     margin: 0;
     padding: 0;
@@ -70,7 +139,7 @@ body,
     margin: 1rem 0;
     padding: 1rem;
     border-radius: 0.75rem;
-    background: #111827;
+    background: #353943;
     color: #f9fafb;
     overflow-x: auto;
 }
diff --git a/frontend/src/components/CategoryTree.vue b/frontend/src/components/CategoryTree.vue
index bf320fb..98e7671 100644
--- a/frontend/src/components/CategoryTree.vue
+++ b/frontend/src/components/CategoryTree.vue
@@ -275,4 +275,53 @@ const handleDeleteCategory = (category) => {
 .subcategories {
     margin-top: 0.25rem;
 }
+
+/* Dark mode overrides */
+:root[data-bs-theme="dark"] .category-header:hover {
+    background-color: #2d3748;
+}
+
+:root[data-bs-theme="dark"] .menu-button {
+    color: #94a3b8;
+}
+
+:root[data-bs-theme="dark"] .menu-button:hover {
+    background-color: rgba(255, 255, 255, 0.08);
+}
+
+:root[data-bs-theme="dark"] .menu-dropdown {
+    background: #2d3748;
+    border-color: #4a5568;
+    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.4);
+}
+
+:root[data-bs-theme="dark"] .menu-item {
+    color: #e2e8f0;
+}
+
+:root[data-bs-theme="dark"] .menu-item:hover {
+    background-color: #374151;
+}
+
+:root[data-bs-theme="dark"] .note-item:hover {
+    background-color: #2d3748;
+}
+
+:root[data-bs-theme="dark"] .note-item.is-pinned {
+    background: #1a3a5c;
+    border-color: #2d6a9f;
+}
+
+:root[data-bs-theme="dark"] .note-item.is-pinned:hover {
+    background: #1e4470;
+}
+
+:root[data-bs-theme="dark"] .note-item.is-featured {
+    background: #3a2e0a;
+    border-color: #7a5a0a;
+}
+
+:root[data-bs-theme="dark"] .note-item.is-featured:hover {
+    background: #453710;
+}
 </style>
diff --git a/frontend/src/components/FileExplorer.vue b/frontend/src/components/FileExplorer.vue
index 4fe0316..fbdc721 100644
--- a/frontend/src/components/FileExplorer.vue
+++ b/frontend/src/components/FileExplorer.vue
@@ -328,4 +328,23 @@ watch(showNewFolderInput, async (v) => {
 .file-item:hover .btn-delete {
     opacity: 1;
 }
+
+/* Dark mode overrides */
+:root[data-bs-theme="dark"] .file-explorer {
+    background: #21252e;
+}
+
+:root[data-bs-theme="dark"] .file-explorer-header {
+    background: #21252e;
+    border-color: #3a3f4b;
+}
+
+:root[data-bs-theme="dark"] .file-item {
+    border-bottom-color: #3a3f4b;
+    color: #e2e8f0;
+}
+
+:root[data-bs-theme="dark"] .file-item:hover {
+    background-color: #2d3748;
+}
 </style>
diff --git a/frontend/src/components/ManageAuthProvidersModal.vue b/frontend/src/components/ManageAuthProvidersModal.vue
index f578f0d..91fee41 100644
--- a/frontend/src/components/ManageAuthProvidersModal.vue
+++ b/frontend/src/components/ManageAuthProvidersModal.vue
@@ -262,4 +262,20 @@ onMounted(loadProviders);
         padding-right: 0.85rem;
     }
 }
+
+/* Dark mode overrides */
+:root[data-bs-theme="dark"] .modal-panel {
+    background: #21252e;
+    border-color: #3a3f4b;
+}
+
+:root[data-bs-theme="dark"] .provider-modal-header {
+    background: linear-gradient(180deg, #2a2f3a 0%, #21252e 100%);
+    border-bottom-color: #3a3f4b;
+}
+
+:root[data-bs-theme="dark"] .provider-section {
+    background: #2a2f3a;
+    border-color: #3a3f4b;
+}
 </style>
diff --git a/frontend/src/components/NoteEditor.vue b/frontend/src/components/NoteEditor.vue
index 5fcb91a..21667b2 100644
--- a/frontend/src/components/NoteEditor.vue
+++ b/frontend/src/components/NoteEditor.vue
@@ -346,4 +346,31 @@ onMounted(async () => {
     color: #7a2727;
     font-size: 0.9rem;
 }
+
+/* Dark mode overrides */
+:root[data-bs-theme="dark"] .editor-toolbar {
+    border-bottom-color: #3a3f4b;
+}
+
+:root[data-bs-theme="dark"] .flag-check {
+    background: #2d3748;
+    border-color: #4a5568;
+}
+
+:root[data-bs-theme="dark"] .preview-pane {
+    background-color: #21252e;
+}
+
+:root[data-bs-theme="dark"] .danger-zone {
+    background: #2d1a1a;
+    border-color: #7a3030;
+}
+
+:root[data-bs-theme="dark"] .danger-zone-title {
+    color: #fc8181;
+}
+
+:root[data-bs-theme="dark"] .danger-zone-copy {
+    color: #fca5a5;
+}
 </style>
diff --git a/frontend/src/components/NoteList.vue b/frontend/src/components/NoteList.vue
index 94ef780..d2e4f27 100644
--- a/frontend/src/components/NoteList.vue
+++ b/frontend/src/components/NoteList.vue
@@ -180,6 +180,10 @@ const getDescription = (note) => {
 
 .note-list--list .note-card:hover {
     transform: none;
+    box-shadow: none;
+    background-color: #eef2ff;
+    border-color: #667eea;
+    border-left: 3px solid #667eea;
 }
 
 .note-list--list .note-title {
@@ -218,4 +222,51 @@ const getDescription = (note) => {
         font-size: 1.45rem;
     }
 }
+
+/* Dark mode overrides */
+:root[data-bs-theme="dark"] .empty-notes-state {
+    border-color: #3a3f4b;
+    background: linear-gradient(180deg, #1e2430 0%, #21252e 100%);
+}
+
+:root[data-bs-theme="dark"] .empty-notes-title {
+    color: #e2e8f0;
+}
+
+:root[data-bs-theme="dark"] .empty-notes-message {
+    color: #94a3b8;
+}
+
+:root[data-bs-theme="dark"] .note-card {
+    border-color: #3a3f4b;
+    background-color: #21252e;
+}
+
+:root[data-bs-theme="dark"] .note-card:hover {
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.4);
+}
+
+:root[data-bs-theme="dark"] .note-list--list .note-card:hover {
+    background-color: #2a2f3a;
+    border-color: #7aa2f7;
+    border-left-color: #7aa2f7;
+}
+
+:root[data-bs-theme="dark"] .note-title {
+    color: #e2e8f0;
+}
+
+:root[data-bs-theme="dark"] .note-preview {
+    color: #94a3b8;
+}
+
+:root[data-bs-theme="dark"] .note-card.is-pinned {
+    background: #1a3a5c;
+    border-color: #2d6a9f;
+}
+
+:root[data-bs-theme="dark"] .note-card.is-featured {
+    background: #3a2e0a;
+    border-color: #7a5a0a;
+}
 </style>
diff --git a/frontend/src/components/NoteViewer.vue b/frontend/src/components/NoteViewer.vue
index 3b80c55..fc3f8b8 100644
--- a/frontend/src/components/NoteViewer.vue
+++ b/frontend/src/components/NoteViewer.vue
@@ -161,8 +161,6 @@ const formatDateTime = (dateString) => new Date(dateString).toLocaleString();
 .markdown-body :deep(pre) {
     padding: 1rem;
     border-radius: 0.75rem;
-    background: #111827;
-    color: #f9fafb;
     overflow-x: auto;
 }
 
@@ -176,4 +174,49 @@ const formatDateTime = (dateString) => new Date(dateString).toLocaleString();
     border-left: 4px solid #748ffc;
     background: #f8f9ff;
 }
+
+/* Dark mode overrides */
+:root[data-bs-theme="dark"] .note-meta {
+    border-bottom-color: #3a3f4b;
+}
+
+:root[data-bs-theme="dark"] .tag-chip {
+    background: #1e2d5f;
+    color: #93b4ff;
+}
+
+:root[data-bs-theme="dark"] .pinned-chip {
+    color: #7dd3fc;
+    background: #1a3a5c;
+    border-color: #2d6a9f;
+}
+
+:root[data-bs-theme="dark"] .featured-chip {
+    color: #fbbf24;
+    background: #3a2e0a;
+    border-color: #7a5a0a;
+}
+
+:root[data-bs-theme="dark"] .public-chip {
+    color: #67e8f9;
+    background: #0c2a3a;
+    border-color: #1d6a7a;
+}
+
+:root[data-bs-theme="dark"] .private-chip {
+    color: #c4b5fd;
+    background: #2d1f5e;
+    border-color: #5b3f9a;
+}
+
+:root[data-bs-theme="dark"] .protected-chip {
+    color: #fdba74;
+    background: #3a1f0a;
+    border-color: #7a4f1a;
+}
+
+:root[data-bs-theme="dark"] .markdown-body :deep(blockquote) {
+    background: #1e2430;
+    color: #94a3b8;
+}
 </style>
diff --git a/frontend/src/components/SearchResultsPage.vue b/frontend/src/components/SearchResultsPage.vue
index 3025853..6c01ce2 100644
--- a/frontend/src/components/SearchResultsPage.vue
+++ b/frontend/src/components/SearchResultsPage.vue
@@ -151,4 +151,34 @@ const goToPage = (page) => {
         flex-direction: column;
     }
 }
+
+/* Dark mode overrides */
+:root[data-bs-theme="dark"] .search-results-header h2 {
+    color: #e2e8f0;
+}
+
+:root[data-bs-theme="dark"] .search-meta {
+    color: #94a3b8;
+}
+
+:root[data-bs-theme="dark"] .page-indicator {
+    color: #94a3b8;
+}
+
+:root[data-bs-theme="dark"] .empty-state {
+    border-color: #3a3f4b;
+    background: radial-gradient(circle at 20% 20%, #1a2035 0%, #1e2430 70%);
+}
+
+:root[data-bs-theme="dark"] .empty-state h3 {
+    color: #e2e8f0;
+}
+
+:root[data-bs-theme="dark"] .empty-state p {
+    color: #94a3b8;
+}
+
+:root[data-bs-theme="dark"] .empty-state-icon {
+    color: #4a6fa5;
+}
 </style>
diff --git a/frontend/src/pages/Admin.vue b/frontend/src/pages/Admin.vue
index 4a92059..ebebb80 100644
--- a/frontend/src/pages/Admin.vue
+++ b/frontend/src/pages/Admin.vue
@@ -919,4 +919,36 @@ onMounted(async () => {
         gap: 0.65rem;
     }
 }
+
+/* Dark mode overrides */
+:root[data-bs-theme="dark"] .admin-topbar {
+    border-bottom-color: #3a3f4b;
+}
+
+:root[data-bs-theme="dark"] .admin-sidebar {
+    background: #21252e;
+    border-right-color: #3a3f4b;
+}
+
+:root[data-bs-theme="dark"] .admin-nav .nav-link {
+    color: #94a3b8;
+}
+
+:root[data-bs-theme="dark"] .admin-nav .nav-link:hover {
+    background: #2d3748;
+    color: #e2e8f0;
+}
+
+:root[data-bs-theme="dark"] .admin-nav .nav-link.active {
+    background: #e2e8f0;
+    color: #1a1d23;
+}
+
+:root[data-bs-theme="dark"] .user-meta-value {
+    color: #94a3b8;
+}
+
+:root[data-bs-theme="dark"] .admin-section {
+    background-color: #21252e;
+}
 </style>