The Toggle Styles tab in the theme settings has two sections, which are not consistent in UX:
1. "Enable optional stylesheets": you check the checkbox to turn the optional stylesheet ON.
2. "Disable module and theme stylesheets": you check the checkbox to turn the stylesheet OFF.
The basic idea of having checkboxes for stylesheets is great. But I did a double-take when I first saw this, and still find it somewhat confusing, since the checkboxes mean two opposite things on the same page. In general, in Drupal, my experience is that checking something means enabling it. So could section 2 be "Enable module and theme stylesheets", where you check to enable just like section 1?