Add styles

style.css

@@ -26,8 +26,9 @@ main {
     grid-template-columns: repeat(4, 1fr);
     grid-template-rows: auto;
     grid-gap: 5px;
-    background: purple;
+    background: #594859;
     padding: 10px;
+    box-shadow: 1px 2px 10px 1px #222;
 }
 
 .screen {
@@ -42,12 +43,31 @@ main {
 button {
     height: 100px;
     width: 100px;
-    font-size: 50px
+    font-size: 50px;
+    border: 1px solid ;
+    box-shadow: 1px 2px 10px 1px #222;
 }
 
-.clear, .back {
+button:hover {
+    filter: brightness(.9);
+}
+
+.num {
+    background: #d9e1f2;
+}
+
+.clear {
     grid-column: span 2;
     width: 205px;
+    background: #f98383;
+}
+
+.operator {
+    background: #ffff69;
+}
+
+.equal {
+    background: #79ff54;
 }
 
 footer {