I thought I'd share a customisation I made for your plugin.
As the Custom CSS textarea fills up with code, the page starts to scroll leading to the 'Save' button disappearing off the screen.
Initially I added a Save button to the bottom of the textarea as well as the top, but that also started to disappear as my custom css code grew.
So I changed the css of the save button to the following:
<input type="submit" class="button-primary" value="<?php _e('Save','mccss'); ?>" style="position: fixed; top: 22PX; right: 0px; z-index: 5; border: 10px solid white; height: 60px; width: 110px; font-size: 20px; "/>
Now it floats always at the top right of the screen (and the button is much larger and easier to click). It saves so much time, and I recommend you add this code (or something similar) to future plugin updates.
Otherwise MANY MANY THANKS for one of the most useful plugins for me! :)