styles: Improve checkbox menu

[shazow]

Minor style improvements:

• Boxes more aligned with labels
• Labels use cursor pointer
• On-hover checkbox background change to indicate hover.

Screenshot:

[shazow]

Tried the transition animation, but it makes the hovering much less obvious when you move your mouse across the options. They don't have time to light up or they're cut off mid-transition, feels glitchy.

[stuartsan]

Gotchya, word. +1!