You still need some design experience and "taste" though.

I've seen some B2B apps which used the Windows look-and-feel and looked absolutely awful: Actions wildly scattered through buttons, menus and context menus, panels and tabs nested several layers deep until the UI started to look like a canyon formation - and no icons or color at all, because I suppose those would have been "unprofessional" - so everything was in dull gray.

(I think it's worth realizing how colorful the stock Windows dialogs and applications actually are through the use of icons, even despite all widgets being gray.)

I still believe the Windows 2000-era UI toolkit is one of the best, because at least it gives you straightforward pathways to build a good-looking and usable UI - but you still have to want to do it.