Hi,
You got it, you should play around with the CSS parameters in the flexibleVM2Global.css.
The correct CSS rule for your case is this:
a#FWcategorynameImage {
display: block;
height: 150px;
padding:10px;
text-align:center;
}
But you would find it in couple seconds, if you were using FireBug plugin(for Firefox).
Firebug plugin is an extremely useful plugin to find the correct CSS rules to make the changes. You can even change some parameters and see the result live in the website without making permanent change in CSS file.
You should start using it.
For more info, visit here:
docs.joomla.org/Tutorial:Using_Firebug_With_Your_Joomla_Website
and watch this video tutorial:
community.joomla.org/videos/firebug_tutorial/firebug_tutorial_part1_english.swf
Cheers.