diff --git a/static/css/components/header.css b/static/css/components/header.css
index 7265974d..3ae3ae8a 100644
--- a/static/css/components/header.css
+++ b/static/css/components/header.css
@@ -329,16 +329,14 @@
 
 .theme-popover {
   display: none;
-  position: absolute;
-  top: calc(100% + 8px);
-  right: -8px;
+  position: fixed;
   background: var(--surface-base, #ffffff);
   border: 1px solid var(--border-base, #e0e0e0);
   border-radius: var(--radius-md, 8px);
   box-shadow: var(--shadow-xl, 0 4px 16px rgba(0, 0, 0, 0.15));
   padding: 12px;
   min-width: 220px;
-  z-index: var(--z-dropdown, 200);
+  z-index: calc(var(--z-overlay) + 1);
   animation: theme-popover-in 0.15s ease-out;
 }
 
diff --git a/static/js/components/Header.js b/static/js/components/Header.js
index 34008baf..9e646f18 100644
--- a/static/js/components/Header.js
+++ b/static/js/components/Header.js
@@ -121,11 +121,11 @@ export class HeaderManager {
       this.updatePopoverActiveStates(currentTheme, currentPreset);
 
       themeToggle.addEventListener('click', (e) => {
-        if (e.target.closest('.theme-popover')) return;
         e.stopPropagation();
         const isOpen = themePopover.classList.contains('active');
         this.closeAllPopovers();
         if (!isOpen) {
+          this.positionThemePopover();
           themePopover.classList.add('active');
         }
       });
@@ -149,6 +149,13 @@ export class HeaderManager {
           themePopover.classList.remove('active');
         }
       });
+
+      // Reposition on resize while popover is active
+      window.addEventListener('resize', () => {
+        if (themePopover.classList.contains('active')) {
+          this.positionThemePopover();
+        }
+      });
     }
 
     closeAllPopovers() {
@@ -158,6 +165,17 @@ export class HeaderManager {
       }
     }
 
+    positionThemePopover() {
+      const themeToggle = document.querySelector('.theme-toggle');
+      const themePopover = document.getElementById('themePopover');
+      if (!themeToggle || !themePopover) return;
+      const rect = themeToggle.getBoundingClientRect();
+      // Guard: toggle may be hidden on narrow viewports (≤950px CSS hides .header-controls)
+      if (rect.width === 0 || rect.height === 0) return;
+      themePopover.style.top = (rect.bottom + 8) + 'px';
+      themePopover.style.right = (window.innerWidth - rect.right - 8) + 'px';
+    }
+
     setThemeMode(mode) {
       setStorageItem('theme', mode);
       const htmlElement = document.documentElement;
diff --git a/templates/components/header.html b/templates/components/header.html
index 7f2cd749..fa106056 100644
--- a/templates/components/header.html
+++ b/templates/components/header.html
@@ -72,55 +72,6 @@
           <i class="fas fa-moon dark-icon"></i>
           <i class="fas fa-sun light-icon"></i>
           <i class="fas fa-adjust auto-icon"></i>
-          <div class="theme-popover" id="themePopover">
-            <div class="theme-popover-section">
-              <div class="theme-popover-label">{{ t('header.theme.mode') }}</div>
-              <div class="theme-popover-modes">
-                <button class="theme-mode-btn" data-mode="light" title="{{ t('header.theme.light') }}">
-                  <i class="fas fa-sun"></i>
-                  <span>{{ t('header.theme.light') }}</span>
-                </button>
-                <button class="theme-mode-btn" data-mode="dark" title="{{ t('header.theme.dark') }}">
-                  <i class="fas fa-moon"></i>
-                  <span>{{ t('header.theme.dark') }}</span>
-                </button>
-                <button class="theme-mode-btn" data-mode="auto" title="{{ t('header.theme.auto') }}">
-                  <i class="fas fa-adjust"></i>
-                  <span>{{ t('header.theme.auto') }}</span>
-                </button>
-              </div>
-            </div>
-            <div class="theme-popover-divider"></div>
-            <div class="theme-popover-section">
-              <div class="theme-popover-label">{{ t('header.theme.presets') }}</div>
-              <div class="theme-popover-presets">
-                <button class="theme-preset-btn" data-preset="default" title="{{ t('header.theme.default') }}">
-                  <span class="preset-swatch preset-swatch-default"></span>
-                  <span>{{ t('header.theme.default') }}</span>
-                </button>
-                <button class="theme-preset-btn" data-preset="nord" title="{{ t('header.theme.nord') }}">
-                  <span class="preset-swatch preset-swatch-nord"></span>
-                  <span>{{ t('header.theme.nord') }}</span>
-                </button>
-                <button class="theme-preset-btn" data-preset="midnight" title="{{ t('header.theme.midnight') }}">
-                  <span class="preset-swatch preset-swatch-midnight"></span>
-                  <span>{{ t('header.theme.midnight') }}</span>
-                </button>
-                <button class="theme-preset-btn" data-preset="monokai" title="{{ t('header.theme.monokai') }}">
-                  <span class="preset-swatch preset-swatch-monokai"></span>
-                  <span>{{ t('header.theme.monokai') }}</span>
-                </button>
-                <button class="theme-preset-btn" data-preset="dracula" title="{{ t('header.theme.dracula') }}">
-                  <span class="preset-swatch preset-swatch-dracula"></span>
-                  <span>{{ t('header.theme.dracula') }}</span>
-                </button>
-                <button class="theme-preset-btn" data-preset="solarized" title="{{ t('header.theme.solarized') }}">
-                  <span class="preset-swatch preset-swatch-solarized"></span>
-                  <span>{{ t('header.theme.solarized') }}</span>
-                </button>
-              </div>
-            </div>
-          </div>
         </div>
         <div class="settings-toggle" title="{{ t('common.actions.settings') }}">
           <i class="fas fa-cog"></i>
@@ -169,6 +120,56 @@
   </div>
 </header>
 
+<div class="theme-popover" id="themePopover" role="dialog" aria-label="{{ t('header.theme.toggle') }}">
+  <div class="theme-popover-section">
+    <div class="theme-popover-label">{{ t('header.theme.mode') }}</div>
+    <div class="theme-popover-modes">
+      <button class="theme-mode-btn" data-mode="light" title="{{ t('header.theme.light') }}">
+        <i class="fas fa-sun"></i>
+        <span>{{ t('header.theme.light') }}</span>
+      </button>
+      <button class="theme-mode-btn" data-mode="dark" title="{{ t('header.theme.dark') }}">
+        <i class="fas fa-moon"></i>
+        <span>{{ t('header.theme.dark') }}</span>
+      </button>
+      <button class="theme-mode-btn" data-mode="auto" title="{{ t('header.theme.auto') }}">
+        <i class="fas fa-adjust"></i>
+        <span>{{ t('header.theme.auto') }}</span>
+      </button>
+    </div>
+  </div>
+  <div class="theme-popover-divider"></div>
+  <div class="theme-popover-section">
+    <div class="theme-popover-label">{{ t('header.theme.presets') }}</div>
+    <div class="theme-popover-presets">
+      <button class="theme-preset-btn" data-preset="default" title="{{ t('header.theme.default') }}">
+        <span class="preset-swatch preset-swatch-default"></span>
+        <span>{{ t('header.theme.default') }}</span>
+      </button>
+      <button class="theme-preset-btn" data-preset="nord" title="{{ t('header.theme.nord') }}">
+        <span class="preset-swatch preset-swatch-nord"></span>
+        <span>{{ t('header.theme.nord') }}</span>
+      </button>
+      <button class="theme-preset-btn" data-preset="midnight" title="{{ t('header.theme.midnight') }}">
+        <span class="preset-swatch preset-swatch-midnight"></span>
+        <span>{{ t('header.theme.midnight') }}</span>
+      </button>
+      <button class="theme-preset-btn" data-preset="monokai" title="{{ t('header.theme.monokai') }}">
+        <span class="preset-swatch preset-swatch-monokai"></span>
+        <span>{{ t('header.theme.monokai') }}</span>
+      </button>
+      <button class="theme-preset-btn" data-preset="dracula" title="{{ t('header.theme.dracula') }}">
+        <span class="preset-swatch preset-swatch-dracula"></span>
+        <span>{{ t('header.theme.dracula') }}</span>
+      </button>
+      <button class="theme-preset-btn" data-preset="solarized" title="{{ t('header.theme.solarized') }}">
+        <span class="preset-swatch preset-swatch-solarized"></span>
+        <span>{{ t('header.theme.solarized') }}</span>
+      </button>
+    </div>
+  </div>
+</div>
+
 <!-- Add search options panel with context-aware options -->
 <div id="searchOptionsPanel" class="search-options-panel hidden">
   <div class="options-header">