Enhanced category-box display component

@oca I made a recent change in core that causes this theme component’s SCSS to fail compilation. The fix is quite simple, these two lines need to be removed from the stylesheet:

@import "common/foundation/variables";
@import "theme_variables";

(The second line causes a SCSS compilation error because that file no longer exists. Both lines are unnecessary, though, the core and theme variables are now injected before any SCSS file is compiled.)