I've found a very easy way to edit CSS files for UBB Threads. Here's how:
Download a copy of
Top Style Pro -it's a demo version which will allow you to run it 25 times.
Go to your Threads main index and using your web browser view source on the page. Cut and paste the source html into a file (call it main_index.htm) and save it.
In the preview pane in Top Style Pro select the htm file of your main index to use as the preview file. Then open a CSS file that you want to edit and as you make changes to it the look of your preview file will change.
I have my main index, postlist, and show flat pages saved as htm files on my PC
