Fix iframe's style to show the focus-ring in demo center.

Author: jeonghee27

demo/style.css

@@ -197,6 +197,10 @@ iframe:focus {
   outline: 5px solid #1E90FF;
 }
 
+iframe:focus-within {
+  outline: 4px #3582ff solid;
+}
+
 a {
   color: #0049bf;
   text-decoration: none;