Add alert css classes

style/main.css

@@ -101,4 +101,24 @@ footer {
     .grid-container {
         grid-template-columns: auto;
     }
+}
+
+.alert {
+    padding: 12px;
+    border: 1px solid transparent;
+}
+.alert-info {
+    color: #0c5460;
+    background-color: #d1ecf1;
+    border-color: #bee5eb;
+}
+.alert-success {
+    color: #155724;
+    background-color: #d4edda;
+    border-color: #c3e6cb;
+}
+.alert-danger {
+    color: #721c24;
+    background-color: #f8d7da;
+    border-color: #f5c6cb;
 }