fix: modal overlay and game screen styling

- Move modal overlay CSS to global stylesheet for reliable overlay behavior
- Render GameCompletionModal outside main container for true overlay effect
- Refactor GameCompletionModal to use global overlay and local content styles
- Fix player score layout, color, and button styling on game detail screen
- Add global .modal and .modal.show classes to index.css
- Clean up CSS modules for modal content and responsive design

Fixes #<issue_number>

src/components/GameCompletionModal.module.css

@@ -2,26 +2,24 @@
     position: fixed;
     top: 0;
     left: 0;
-    width: 100%;
-    height: 100%;
-    background-color: rgba(0, 0, 0, 0.7);
-    z-index: 1000;
-    display: none;
+    width: 100vw;
+    height: 100vh;
+    background-color: rgba(0, 0, 0, 0.8);
+    z-index: 9999;
+    display: flex;
     justify-content: center;
     align-items: center;
 }
-#game-completion-modal.show {
-    display: flex;
-}
-#game-completion-modal .modal-content {
-    background-color: #2a2a2a;
-    padding: 30px;
-    border-radius: 10px;
-    width: 90%;
-    max-width: 500px;
+.modal-content {
+    background-color: #222;
+    padding: 32px 24px 24px 24px;
+    border-radius: 16px;
+    width: 90vw;
+    max-width: 480px;
+    box-shadow: 0 4px 32px rgba(0,0,0,0.7);
     position: relative;
     margin: auto;
-    transform: translateY(0);
+    transform: none;
 }
 .final-scores {
     margin: 20px 0;
@@ -30,56 +28,88 @@
     display: flex;
     justify-content: space-between;
     align-items: center;
-    padding: 20px;
-    margin-bottom: 10px;
+    padding: 18px 0;
+    margin-bottom: 8px;
     background: #333;
-    border-radius: 5px;
-    font-size: 24px;
+    border-radius: 8px;
+    font-size: 1.2rem;
+    color: #fff;
 }
 .final-score .player-name {
-    font-size: 24px;
+    font-size: 1.2rem;
     font-weight: bold;
-    color: white;
+    color: #fff;
 }
 .final-score .score {
-    font-size: 24px;
+    font-size: 1.2rem;
     font-weight: bold;
-    color: white;
+    color: #fff;
 }
 .winner-announcement {
     text-align: center;
-    margin: 20px 0;
-    padding: 20px;
-    background: #4CAF50;
-    border-radius: 5px;
+    margin: 20px 0 0 0;
+    padding: 18px 8px;
+    background: #43a047;
+    border-radius: 8px;
+    font-size: 1.2rem;
+    color: #fff;
+    font-weight: 700;
 }
 .winner-announcement h3 {
-    font-size: 24px;
+    font-size: 1.2rem;
     margin: 0;
-    color: white;
+    color: #fff;
 }
-.modal-buttons {
+.modal-footer {
     display: flex;
-    gap: 10px;
-    margin-top: 20px;
+    flex-direction: row;
+    gap: 16px;
+    margin-top: 24px;
+    width: 100%;
+    justify-content: center;
 }
-.modal-buttons .btn {
+.btn {
     flex: 1;
-    padding: 20px;
-    font-size: 20px;
+    padding: 18px 0;
+    font-size: 1.1rem;
     border: none;
-    border-radius: 0;
+    border-radius: 8px;
     cursor: pointer;
-    color: white;
+    color: #fff;
+    background: #333;
+    font-weight: 600;
+    transition: background 0.2s;
 }
-.modal-buttons .btn--warning {
+.btn--warning {
     background: #f44336;
 }
-.modal-buttons .btn:not(.btn--warning) {
-    background: #333;
+.btn:not(.btn--warning):hover {
+    background: #444;
 }
-#game-completion-modal h2 {
-    font-size: 24px;
-    margin-bottom: 20px;
-    color: white;
+.btn--warning:hover {
+    background: #d32f2f;
+}
+.close-button {
+    position: absolute;
+    top: 12px;
+    right: 16px;
+    background: none;
+    border: none;
+    color: #aaa;
+    font-size: 2rem;
+    cursor: pointer;
+    z-index: 2;
+}
+.close-button:hover {
+    color: #fff;
+}
+@media (max-width: 600px) {
+    .modal-content {
+        padding: 16px 4px 16px 4px;
+        max-width: 98vw;
+    }
+    .btn {
+        font-size: 1rem;
+        padding: 14px 0;
+    }
 }