Improve responsiveness

css/main.css

@@ -140,6 +140,18 @@ a.detail:hover {
 }
 
 @media (max-width: 480px) {
+    a.btn {
+        width: 8em;
+        height: 8em;
+    }
+
+    main {
+        column-gap: 2em;
+        margin: 2em;
+    }
+}
+
+@media (max-width: 310px) {
     main {
         grid-template-columns: repeat(1, min-content);
     }