Update style.css

style.css

@@ -95,13 +95,14 @@ button:hover {
   border-radius: 8px;
 }
 
+/* Cells */
 .cell {
   width: 100%;
-  height: 100%;
   aspect-ratio: 1 / 1;
   background-color: #fff;
   cursor: pointer;
   transition: background-color 0.2s ease;
+  box-sizing: border-box;
 }
 
 .cell:hover {
@@ -111,6 +112,7 @@ button:hover {
 .cell.filled {
   background-color: #007aff;
   border: 1px solid #005bb5;
+  box-sizing: border-box;
 }
 
 /* Stats */