Hi Amy,

If you used CSS compression in Template Options > Adnavced - disable that, clear Joomla cache and you can turn it on again or keep disabled. If you never used that and CSS compression is not enabled, Joomla or Template by default do not cache any CSS files.

But extra rules in .htaccess may do that.

If you used Custom CSS in Template Options > Custom Code > Custom CSS - that code is never cached, becuase it's used/displayed inside HTML code.

The last thing. I hope you didn't edit template.css file, otherwise indeed, all changes are removed. But we informed about that in Helix documenation. Who didn't read, his fault ;p