@charset "UTF-8";
/* CSS Document */

.hidden { display: none; }
 .unhidden { display: block; }
If you want to use visibility, then change these classes to:

.hidden { visibility: hidden; }
 .unhidden { visibility: visible; }
Then add the hidden class to your DIV so that it starts out as hidden on the page:

<div id="learnHTML" class="hidden">