fix: textarea border and placeholder color in dark theme

Author: fzzv

components/retroui/Textarea.tsx

@@ -1,4 +1,5 @@
 import React from "react";
+import { cn } from "@/lib/utils";
 
 export function Textarea({
   type = "text",
@@ -10,7 +11,10 @@ export function Textarea({
     <textarea
       placeholder={placeholder}
       rows={4}
-      className={`px-4 py-2 w-full border-2 border-black shadow-md transition focus:outline-hidden focus:shadow-xs ${className}`}
+      className={cn(
+        "px-4 py-2 w-full border-2 border-border shadow-md transition focus:outline-hidden focus:shadow-xs placeholder:text-muted-foreground",
+        className
+      )}
       {...props}
     />
   );