- Added full-height flex layout with fixed header and centered main content.

- Locked page scroll via body overflow hidden to prevent outer page scrolling.
- Moved game content into scrollable middle pane.
- Removed global top padding from styles.css to match new fixed-header layout.
- Simplified layout structure and removed unused commented code.

src/tictactoe/styles.css

@@ -3,7 +3,6 @@ body {
   background: #eaeef3;
   display: flex;
   justify-content: center;
-  padding-top: 50px;
   margin: 0;
   color: #222;
 }