It's potentially silly because, well, I can't find it.
When I go to the plugin editor i'm given these
boxer/wpboxer.php
boxer/framework/functions.php
boxer/framework/cow_plugin_framework.php
boxer/framework/timthumb.php
boxer/templates/dummy.css
boxer/templates/capslide.js
boxer/views/block_options.php
boxer/views/donate.php
boxer/views/settings.php
boxer/readme.txt
None of which are the css that I need to change. When I make changes on to the boxes, nothing happens, so I want to get into the css and do it from there.