XF 1.5 Additional CSS to calltoaction button?


I created a new call to action button (for creating a new thread) and wish to apply some additional CSS to it (don't want it to look like other calltoaction buttons). How do I do that? I tried putting additional CSS in Extra.css and then changing the following
<a href="{xen:link misc/new-thread}" class="callToAction OverlayTrigger">
I changed the callToAction class to the new css styling but once I do that it removes all styling from the button.