You can right click on your CSS file and select Properties to identify which topics are associated with it but I am not aware of a way inside RH where you can identify a specific CSS file style. I think you'll have to do a global find on the topics you identify using the technique I've mentioned to find the relevant style.
Read the RoboColum(n) for mutterings on RoboHelp, Technical Communication Suite and technical communication.
Depending on the style, a multi file find and replace search on
<tagname> (such as <h1>
will find all the topics using the tag or class. The built in tool also allows you to click View for each of the topics listed after the search.
See www.grainge.org for RoboHelp and Authoring tips
You're a star Peter. That's worked a treat.
I haven't used the Multi-File Find and Replace for a long time. It didn't cross my mind to use it for finding a style!