Current CSS is mostly handcrafted, i.e. we aren't using any preprocessor such as SASS or LESS. This leads to a lot of redundant css with properties not being shared among skins and extensions.
Description and Documentation
This will also change the way skins load their css into the page, i.e. how PatternSkin is customized: instead of cascading different css files individually will there be a SASS compiler generating a derived single css file from the skin's base definitions together with any user changes such as modifying the colorset or the icon set.