Fix window transparency and theme dropdown background issues

- Fixed chat footer background to use var(--surface) CSS variable instead of hardcoded colors, ensuring proper theme adaptation
- Fixed theme dropdown background by changing from var(--input-bg) to var(--surface) in theme-sentient.css
- Added CSS override rules in desktop.css to ensure dropdown uses correct background
- Added JavaScript fix in theme-manager.js to automatically apply correct dropdown background on theme load

This resolves issues where theme dropdown and chat footer had black backgrounds in light themes.

ui/suite/css/desktop.css

@@ -283,3 +283,10 @@ body.window-maximized .window-element {
     background-color: var(--surface, #ffffff) !important;
     opacity: 1 !important;
 }
+
+/* Fix theme dropdown background - use surface color to adapt to theme */
+/* This overrides hardcoded black background from other CSS files */
+#themeDropdown,
+select.theme-dropdown {
+    background: var(--surface) !important;
+}

ui/suite/css/theme-sentient.css

@@ -876,7 +876,7 @@
 [data-theme="sentient"] input,
 [data-theme="sentient"] textarea,
 [data-theme="sentient"] select {
-    background: var(--input-bg);
+    background: var(--surface);
     border: 1px solid var(--input-border);
     color: var(--text);
     border-radius: 8px;
@@ -884,6 +884,12 @@
     transition: all 0.2s ease;
 }
 
+/* Ensure theme dropdown uses surface color in all themes */
+[data-theme="sentient"] select.theme-dropdown,
+[data-theme="sentient"] #themeDropdown {
+    background: var(--surface) !important;
+}
+
 [data-theme="sentient"] input:focus,
 [data-theme="sentient"] textarea:focus,
 [data-theme="sentient"] select:focus {

ui/suite/js/theme-manager.js

@@ -263,6 +263,22 @@ const ThemeManager = (() => {
           primary: primary,
         });
         updateDropdown();
+
+        // Fix theme dropdown background to use surface color
+        const themeDropdown = document.getElementById("themeDropdown");
+        if (themeDropdown) {
+          const surfaceColor = getComputedStyle(document.documentElement)
+            .getPropertyValue("--surface")
+            .trim();
+          if (surfaceColor) {
+            themeDropdown.style.setProperty(
+              "background",
+              surfaceColor,
+              "important",
+            );
+          }
+        }
+
         subscribers.forEach((cb) => cb({ themeId: id, themeName: theme.name }));
       }, 50);
     };