Fix N-Queens board issues

Fixes the disappearing board when the timer starts and increases the board size.

src/components/NQueensPuzzle.tsx

@@ -269,10 +269,11 @@ const NQueensPuzzle: React.FC<NQueensPuzzleProps> = ({ showSocialShare = false }
           <div className="lg:col-span-2 flex justify-center">
             <div className="inline-block">
               <div 
-                className="grid border-2 border-border"
+                className="grid border-2 border-border bg-background"
                 style={{ 
                   gridTemplateColumns: `repeat(${currentBoardSize}, 1fr)`,
-                  aspectRatio: '1'
+                  width: '500px',
+                  height: '500px'
                 }}
               >
                 {Array.from({ length: currentBoardSize }, (_, row) =>