Make selection required

Author: lulunac27a

index.html

@@ -17,7 +17,7 @@ <h1>Dice Game Web App</h1>
             required
         /><br />
         <!--button to use normal dice or custom dice mode-->Dice mode:
-        <select id="diceMode">
+        <select id="diceMode" required>
             <option value="normal" selected>Normal</option>
             <option value="custom">Custom</option>
         </select>