This style will change default forum theme (def342) to the clean one. It deletes all unnecessary content from forum like:

- description of categories
- forum footer
- welcome box
- cookie box
- awards
- graphical backgrounds of buttons
- facebook, steam and others like that box
- unnecessary borders

Things changed:

- hover on table row (topics and categories)
- color, most of things are grey now
- the thing I like the most: header which has fixed position - always on top of screen (like a one in facebook)

And other minor changes which I don't remember.