
Only in rare cases could you need a browser specific stylesheet.
Rarely there have been cases I have to do browser specific stylesheets. And if your styleNN.css is a copy of your style.css you might as well delete styleNN.css, even the IE bugs can be dealt in style.css.
In the case of some themes I make there are 3 stylesheets but they are not browser specific, they are divided according to content. 1) Basic layout 2) Block layout 3) Module content layout. It depends on the designer.
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