Fix horizontal centering for better balanced layout

Co-authored-by: SweetCodey <167379283+SweetCodey@users.noreply.github.com>

Author: Copilot

src/FlappyBird.css

@@ -4,6 +4,9 @@
   padding: 20px;
   text-align: center;
   font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', sans-serif;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
 }
 
 .flappy-bird-container h1 {
@@ -15,7 +18,6 @@
 
 .game-area {
   position: relative;
-  display: inline-block;
   margin-bottom: 20px;
   border-radius: 10px;
   box-shadow: 0 8px 32px rgba(0,0,0,0.2);