diff --git a/static/app.js b/static/app.js
index 240d41c..2c999cf 100644
--- a/static/app.js
+++ b/static/app.js
@@ -1,4 +1,45 @@
 (() => {
+  // Theme management
+  const themeToggle = document.getElementById("themeToggle");
+  const prefersDark = window.matchMedia("(prefers-color-scheme: dark)");
+
+  function getTheme() {
+    const saved = localStorage.getItem("xp-theme");
+    if (saved) return saved;
+    return prefersDark.matches ? "dark" : "light";
+  }
+
+  function setTheme(theme) {
+    if (theme === "dark") {
+      document.documentElement.setAttribute("data-theme", "dark");
+      if (themeToggle) themeToggle.textContent = "☀️";
+    } else {
+      document.documentElement.removeAttribute("data-theme");
+      if (themeToggle) themeToggle.textContent = "🌙";
+    }
+    localStorage.setItem("xp-theme", theme);
+  }
+
+  function toggleTheme() {
+    const current = document.documentElement.getAttribute("data-theme") === "dark" ? "dark" : "light";
+    setTheme(current === "dark" ? "light" : "dark");
+  }
+
+  // Initialize theme
+  setTheme(getTheme());
+
+  // Listen for theme toggle
+  if (themeToggle) {
+    themeToggle.addEventListener("click", toggleTheme);
+  }
+
+  // Listen for system theme changes
+  prefersDark.addEventListener("change", (e) => {
+    if (!localStorage.getItem("xp-theme")) {
+      setTheme(e.matches ? "dark" : "light");
+    }
+  });
+
   let qs = new URLSearchParams(window.location.search);
   const qInput = document.getElementById("q");
   const channelDropdown = document.getElementById("channelDropdown");
diff --git a/static/index.html b/static/index.html
index d3fe8cd..1742882 100644
--- a/static/index.html
+++ b/static/index.html
@@ -13,6 +13,7 @@
       <div class="title-bar">
         <div class="title-bar-text">This Little Corner — Elastic Search</div>
         <div class="title-bar-controls">
+          <button id="themeToggle" aria-label="Toggle theme" title="Toggle dark mode" style="margin-right: 4px; min-width: 24px; font-size: 14px;">🌙</button>
           <button aria-label="Minimize"></button>
           <button aria-label="Maximize"></button>
           <button aria-label="Close"></button>
diff --git a/static/style.css b/static/style.css
index 08ddc4e..526f992 100644
--- a/static/style.css
+++ b/static/style.css
@@ -1,5 +1,101 @@
 /* Custom styles for XP.css integration */
 
+/* Theme variables - Light mode (default) */
+:root {
+  --xp-bg-desktop: teal;
+  --xp-bg-window: #ece9d8;
+  --xp-bg-white: white;
+  --xp-text-primary: black;
+  --xp-text-secondary: #666;
+  --xp-border-light: white;
+  --xp-border-dark: #0a0a0a;
+  --xp-border-shadow: grey;
+  --xp-border-highlight: #dfdfdf;
+  --xp-button-face: #ece9d8;
+  --xp-titlebar-bg: linear-gradient(to right, #0054e3, #1591e6);
+  --xp-titlebar-text: white;
+  --xp-selection-bg: #0a246a;
+  --xp-selection-text: white;
+  --xp-field-bg: white;
+  --xp-field-border: #7f9db9;
+}
+
+/* Dark mode theme */
+[data-theme="dark"] {
+  --xp-bg-desktop: #1a1a2e;
+  --xp-bg-window: #2d2d44;
+  --xp-bg-white: #1e1e2e;
+  --xp-text-primary: #e0e0e0;
+  --xp-text-secondary: #a0a0a0;
+  --xp-border-light: #4a4a5e;
+  --xp-border-dark: #0a0a0a;
+  --xp-border-shadow: #1a1a1a;
+  --xp-border-highlight: #3a3a4e;
+  --xp-button-face: #2d2d44;
+  --xp-titlebar-bg: linear-gradient(to right, #1a3a5e, #2a4a6e);
+  --xp-titlebar-text: #e0e0e0;
+  --xp-selection-bg: #2a4a7e;
+  --xp-selection-text: white;
+  --xp-field-bg: #1e1e2e;
+  --xp-field-border: #4a5a6e;
+}
+
+/* Apply theme variables */
+body {
+  background: var(--xp-bg-desktop);
+  color: var(--xp-text-primary);
+}
+
+.window {
+  background: var(--xp-bg-window);
+}
+
+.window-body {
+  background: var(--xp-bg-window);
+  color: var(--xp-text-primary);
+}
+
+.title-bar {
+  background: var(--xp-titlebar-bg);
+  color: var(--xp-titlebar-text);
+}
+
+button {
+  background: var(--xp-button-face);
+  color: var(--xp-text-primary);
+  box-shadow: inset -1px -1px var(--xp-border-dark),
+              inset 1px 1px var(--xp-border-light),
+              inset -2px -2px var(--xp-border-shadow),
+              inset 2px 2px var(--xp-border-highlight);
+}
+
+button:active {
+  box-shadow: inset -1px -1px var(--xp-border-light),
+              inset 1px 1px var(--xp-border-dark),
+              inset -2px -2px var(--xp-border-highlight),
+              inset 2px 2px var(--xp-border-shadow);
+}
+
+input[type="text"],
+textarea,
+select {
+  background: var(--xp-field-bg);
+  color: var(--xp-text-primary);
+  border-color: var(--xp-field-border);
+}
+
+fieldset {
+  border-color: var(--xp-border-shadow) var(--xp-border-light) var(--xp-border-light) var(--xp-border-shadow);
+}
+
+.status-bar {
+  background: var(--xp-bg-window);
+}
+
+.status-bar-field {
+  color: var(--xp-text-primary);
+}
+
 /* Fix blurry text rendering - override XP.css font smoothing */
 .window,
 .window *,
@@ -33,10 +129,18 @@ label {
   font-size: 11px;
 }
 
-body {
-  background: teal;
-  padding: 0;
-  margin: 0;
+/* Smooth theme transitions */
+body,
+.window,
+.window-body,
+button,
+input,
+select,
+textarea,
+.status-bar,
+.channel-dropdown summary,
+.channel-options {
+  transition: background 0.3s ease, color 0.3s ease, border-color 0.3s ease;
 }
 
 /* Channel dropdown custom styling */
@@ -49,9 +153,10 @@ body {
   list-style: none;
   cursor: pointer;
   padding: 3px 4px;
-  background: ButtonFace;
+  background: var(--xp-button-face);
+  color: var(--xp-text-primary);
   border: 1px solid;
-  border-color: ButtonHighlight ButtonShadow ButtonShadow ButtonHighlight;
+  border-color: var(--xp-border-light) var(--xp-border-shadow) var(--xp-border-shadow) var(--xp-border-light);
   min-width: 180px;
   text-align: left;
 }
@@ -74,12 +179,13 @@ body {
   position: absolute;
   margin-top: 2px;
   padding: 4px;
-  background: ButtonFace;
+  background: var(--xp-bg-window);
+  color: var(--xp-text-primary);
   border: 1px solid;
-  border-color: ButtonHighlight ButtonShadow ButtonShadow ButtonHighlight;
+  border-color: var(--xp-border-light) var(--xp-border-shadow) var(--xp-border-shadow) var(--xp-border-light);
   max-height: 300px;
   overflow-y: auto;
-  box-shadow: 2px 2px 0 rgba(0, 0, 0, 0.2);
+  box-shadow: 2px 2px 0 rgba(0, 0, 0, 0.3);
   z-index: 100;
   min-width: 220px;
 }
@@ -116,7 +222,7 @@ body {
 
 /* Results styling */
 #results .item {
-  border-bottom: 1px solid ButtonShadow;
+  border-bottom: 1px solid var(--xp-border-shadow);
   padding: 12px 0;
   margin-bottom: 8px;
 }
@@ -144,9 +250,10 @@ body {
 
 /* Transcript and highlights */
 .transcript {
-  background: Window;
+  background: var(--xp-field-bg);
+  color: var(--xp-text-primary);
   border: 1px solid;
-  border-color: ButtonShadow ButtonHighlight ButtonHighlight ButtonShadow;
+  border-color: var(--xp-border-shadow) var(--xp-border-light) var(--xp-border-light) var(--xp-border-shadow);
   padding: 8px;
   margin-top: 6px;
   max-height: 200px;
@@ -169,9 +276,9 @@ body {
 }
 
 .highlight-row:hover {
-  background: Highlight;
-  color: HighlightText;
-  border: 1px dotted WindowText;
+  background: var(--xp-selection-bg);
+  color: var(--xp-selection-text);
+  border: 1px dotted var(--xp-text-primary);
 }
 
 mark {
@@ -187,9 +294,10 @@ mark {
 .full-transcript {
   margin-top: 12px;
   padding: 8px;
-  background: Window;
+  background: var(--xp-field-bg);
+  color: var(--xp-text-primary);
   border: 2px solid;
-  border-color: ButtonShadow ButtonHighlight ButtonHighlight ButtonShadow;
+  border-color: var(--xp-border-shadow) var(--xp-border-light) var(--xp-border-light) var(--xp-border-shadow);
   max-height: 400px;
   overflow-y: auto;
   font-size: 11px;
@@ -198,7 +306,7 @@ mark {
 .transcript-segment {
   margin-bottom: 10px;
   padding-bottom: 6px;
-  border-bottom: 1px solid ButtonShadow;
+  border-bottom: 1px solid var(--xp-border-shadow);
 }
 
 .transcript-segment:last-child {
@@ -241,7 +349,7 @@ mark {
 }
 
 .transcript-text {
-  color: WindowText;
+  color: var(--xp-text-primary);
   line-height: 1.4;
 }
 
@@ -251,8 +359,8 @@ mark {
   display: flex;
   align-items: center;
   justify-content: space-between;
-  background: ActiveCaption;
-  color: CaptionText;
+  background: var(--xp-titlebar-bg);
+  color: var(--xp-titlebar-text);
   padding: 2px 4px;
 }
 
@@ -264,8 +372,8 @@ mark {
 }
 
 .transcript-close:hover {
-  background: Highlight;
-  color: HighlightText;
+  background: var(--xp-selection-bg);
+  color: var(--xp-selection-text);
 }
 
 /* Chart styling */
@@ -283,7 +391,7 @@ mark {
 }
 
 #frequencyChart .axis text {
-  fill: WindowText;
+  fill: var(--xp-text-primary);
   font-size: 10px;
 }