I really don't know why this hasn't been implemented but it surely seems simple and would have a HUGE impact on the CSS coders everywhere.
So instead of doing this...
.selector .subselector{property:attribute;}
.selector .anothersubselector{property:attribute;}
Why not this?
.selector{{
.subselector{property:attribute;}
.anothersubselector{property:attribute;}
}}
Pure. Simple. And it will increase CSS readability and cut down of file size because you wont have to repeat the lead selector 100 times...