style: update style

style.css

@@ -1,12 +1,14 @@
 body,
 html {
   font-family: Arial, sans-serif;
+  box-sizing: border-box;
+  margin: 0;
 }
 
 main {
-  padding: 10px 20px;
+  padding: 2rem;
   max-width: 48rem;
-  height: 100dvh;
+  height: max(calc(100dvh - 4rem), 800px);
   margin-left: auto;
   margin-right: auto;
   display: flex;
@@ -129,7 +131,7 @@ button:hover:not(:disabled) {
 }
 
 .card {
-  background-color: #c3dffc;
+  background-color: #deeeff;
   padding: 2rem;
   border-radius: 1rem;
   border: 1px solid #94c6fb;
@@ -157,3 +159,10 @@ button:hover:not(:disabled) {
   background-color: #deeeff;
   color: rgb(0, 0, 0);
 }
+
+
+@media only screen and (max-width: 600px) {
+  .card {
+    flex-direction: column;
+  }
+}