There are a couple of problems with that.
First, and most importantly, Eclipse cannot do style suggestions for
any sort of page definition as far as I can tell, including html and
jsp pages. Part of the reason for that is that the Eclipse
J2EE plugins don't assume that they know where CSS definitions are. A plugin would have to scan the CSS sources and digest them into something that could be popped up at computer speeds to be useful. And know what to scan.
Which leads to another problem. Not all the CSS you'll see is patently defined. If you use an extension tag library like RichFaces or IceFaces, then there are a whole raft of additional styles introduced internally to those tagsets. And if that wasn't enough, some web browsers have their own internally-defined CSS classes, which vary depending on browser and browser version. Just because they're defined internally doesn't mean that you cannot use them (and in some cases, even redefine them).
Then there's the issue that in JSF, the attribute that references CSS classes in JSF HTML tags is "styleClass", not "style", so you'd have to have an additional hook in the J2EE plugins to allow for that.
So what I do is flip back and forth to the style definition files and use the Outline View to present me with the style names.
Incidentally, I don't recommend using raw HTML in JSF View Templates. Instead of a DIV, I'd recommend a 1x1 cell panelGrid.