Use blue bg for DocSearch button in dark mode

Change .DocSearch-Button-Key dark mode background from gray-700 to blue-400 in src/styles/tailwind.css to adjust the button appearance in dark theme (improves visibility/brand consistency).

Author: Deven14125

src/styles/tailwind.css

@@ -48,7 +48,7 @@
   @apply hidden! lg:flex!;
 }
 .DocSearch-Button-Key {
-  @apply text-gray-700! bg-gray-100! border-gray-300! dark:text-gray-100! dark:bg-gray-700! dark:border-gray-500!;
+  @apply text-gray-700! bg-gray-100! border-gray-300! dark:text-gray-100! dark:bg-blue-400! dark:border-gray-500!;
 }
 .DocSearch-Button .DocSearch-Search-Icon {
   @apply text-white! lg:text-gray-100!;