Fix missing attribute in role-required-states example

_rules/role-required-states-and-properties-4e8ab6.md

@@ -79,7 +79,7 @@ This `heading` has the required `aria-level` property.
 This `checkbox` has the required `aria-checked` property.
 
 ```html
-<div role="checkbox" aria-checked="false"></div>
+<div role="checkbox" aria-checked="false" aria-labelledby="label"></div>
 <div id="label">Check me</div>
 ```