Reload the theme perhaps... its embedded into the file after first use.
- Make sure no layouts are using the theme you are trying to edit the css for.
- Delete that particular theme from your file (manage themes).
- Reapply the theme to a layout (your edits will now show up)
- Additionally you can copy and paste the object then onto your own custom theme layout and save the style edits into your own custom theme.
p.s. If anyone knows how to make that Popup Menu tick box look more professional yell out ;) Its even the wrong colour for the selected item (goes inverse and almost invisible - bug).