[DiapDealer]

Sigil already provides a css validation feature that will identify syntax errors like yours in css.

As to Sigil's error finder: there really isn't one. Sigil has basically taken itself out of the syntax validation game. Sigil 's Well-Formed Check is just that. It's only the most basic of checks to make sure code is machine parsable. It only checks to make sure that all opening tags are properly closed and makes sure no illegal nesting of tags is occurring, but that's about it.

But Sigil does allow for 3rd-party validation plugins (there's one for EpubCheck), and it uses the W3C online validation tool to allow users to validate their css (against different css levels that are configurable in Sigil's preferences). The css validation tool is found in the menu under Tools->Validate Stylesheets with W3C. Users find it invaluable for discovering simple, but often overlooked, syntax errors. They use it precisely because Adobe's RMSDK will bail on everything when it encounters any syntax errors whatsoever. Other rendering engines tend to be more forgiving.