You can do this through straight javascript and DOM, but I really recommend learning JQuery. Here is a function you can use to actually toggle that object.
EDIT: Adding the actual code:
Solution:
HTML snippet:
<a href="#" id="showAll" title="Show Tags">Show All Tags</a>
<ul id="tags" class="subforums" style="display:none;overflow-x: visible; overflow-y: visible; ">
<li>Tag 1</li>
<li>Tag 2</li>
<li>Tag 3</li>
<li>Tag 4</li>
<li>Tag 5</li>
</ul>
Javascript code using JQuery from Google's Content Distribution Network: https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js
$(function() {
$('#showAll').click(function(){ //Adds click event listener
$('#tags').toggle('slow'); // Toggles visibility. Use the 'slow' parameter to add a nice effect.
});
});
You can test directly from this link: http://jsfiddle.net/vssJr/5/
Additional Comments on JQuery:
Someone has suggested that using JQuery for something like this is wrong because it is a 50k Library. I have a strong opinion against that.
JQuery is widely used because of the huge advantages it offers (like many other javascript frameworks). Additionally, JQuery is hosted by Content Distribution Networks (CDNs) like Google's CDN that will guarantee that the library is cached in the client's browser. It will have minimal impact on the client.
Additionally, with JQuery you can use powerful selectors, adding event listener, and use functions that are for the most part guaranteed to be cross-browser.
If you are a beginner and want to learn Javascript, please don't discount frameworks like JQuery. It will make your life so much easier.