fix: add dark mode support to text selection menu

Updates text selection menu styling to support dark theme with proper background colors and border styles for improved visibility in both light and dark modes.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: milisp

src/components/chat/TextSelectionMenu.tsx

@@ -112,7 +112,7 @@ export const TextSelectionMenu: React.FC<TextSelectionMenuProps> = () => {
         pointerEvents: 'auto'
       }}
     >
-      <div className="bg-white rounded-lg shadow-lg border border-gray-200 p-1 flex items-center gap-1">
+      <div className="bg-white dark:bg-gray-800 rounded-lg shadow-lg border border-gray-200 dark:border-gray-700 p-1 flex items-center gap-1">
         <Button
           variant="ghost"
           size="sm"
@@ -123,7 +123,7 @@ export const TextSelectionMenu: React.FC<TextSelectionMenuProps> = () => {
           Copy
         </Button>
 
-        <div className="w-px h-4 bg-gray-300" />
+        <div className="w-px h-4 bg-gray-300 dark:bg-gray-600" />
 
         <Popover open={isOpen} onOpenChange={setIsOpen}>
           <PopoverTrigger asChild>
@@ -195,8 +195,8 @@ export const TextSelectionMenu: React.FC<TextSelectionMenuProps> = () => {
 
       {/* Arrow pointing down to selection */}
       <div className="absolute top-full left-1/2 transform -translate-x-1/2">
-        <div className="w-0 h-0 border-l-4 border-r-4 border-t-4 border-l-transparent border-r-transparent border-t-gray-200"></div>
-        <div className="w-0 h-0 border-l-3 border-r-3 border-t-3 border-l-transparent border-r-transparent border-t-white absolute top-0 left-1/2 transform -translate-x-1/2 -translate-y-px"></div>
+        <div className="w-0 h-0 border-l-4 border-r-4 border-t-4 border-l-transparent border-r-transparent border-t-gray-200 dark:border-t-gray-700"></div>
+        <div className="w-0 h-0 border-l-3 border-r-3 border-t-3 border-l-transparent border-r-transparent border-t-white dark:border-t-gray-800 absolute top-0 left-1/2 transform -translate-x-1/2 -translate-y-px"></div>
       </div>
     </div>
   );