This question seems to have already been discussed but you are more specifically talking about a CSS Editor. And I am sure that's why they haven't marked your question as duplicated.
However, what I can suggest you is the usage of several tools which I have posted in answers to other questions, like this: Dreamweaver alternative in ubuntu?, and even when I can bet that you have already seen it, I transcript it here for your convenience:
Your question seems to be a little bit ambiguous.
First of all and related to the alternative to Dreamweaver, I found
all the suggestions of all the other answers excellent, but when
looking for an alternative to Dreamweaver, the closest application
-for me- it was the Amaya Project. Which seems to be richest than
other alternatives and a little bit more sophisticated than the
A screenshot from the official web is here for you to see it in
Additional screenshots can be reached by clicking the next link:
You may find it a little bit unstable, or at least it was for me but
it may also fit your needs.
After playing with WYSIWYG editors, I prefered direct encoding with
BlueFish but it is not a WYSIWYG editor.
And about the suggestions for your issue with the firebug I can't say
Please let us know how did you do if you give Amaya a chance.
== After installing Amaya, I find it yet far from stable but somehow
it seems to have a better features than other applications, if you
consider that other software are simple Text Editors and Amaya is like
a WYSIWYG editor.
I tested what you said in your comment and I found that Amaya don't
even get noticed that something changed in the files/folders
structure/name. Which won't fit your needs related to this.
In the next screenshot you can see I renamed the "resources" folder to
"resources1" and Amaya is yet showing it as "resources" and there is
no way to force it refresh. Even after restarting the software and
loading the project again, Amaya won't notice it.
I am going to follow your question closely hoping somebody come and
drop a good alternative.
Also, in the answers of other users to the same questions I found the "Blue Griffon Web Editor" which seems to be the only stable web editor that features a real time preview window, that -btw- can't be seen in split mode. You can only see the code or the WYSIWYG preview, not both at the same time.
Screenshots placed here for your convenience:
This tool includes lots of useful tools but some of the add-ons or plugins may be non-free (paid). Which reduces the attraction to it.
The Aptana Studio 3, which I reccomend in this answer: Basic Web Development IDE/Editor like Dreamweaver? is -for me- the best tool for programming, since I can live preview using a web browser in my dual view extended desktop. Which may be not your case.
That's what I can suggest. Sorry if this don't fit your needs and...