<a id="my_show_search_box_button" href="#" onclick="document.getElementById('my_show_search_box_button').style.display='block'; document.getElementById('my_optional_container').style.display='block';" >Display it</a>
<div id="my_optional_container" class="my_optional_container" style="display:none">
<!-- Hidden content here -->
</div>
Feel free to comment if you can add help to this page or point out issues and solutions you have found. I do not provide support on this site, if you need help with a problem head over to stack overflow.