Improve checkbox component

[dstrukt]

• Increase checkbox size & states

Still debating if I want the checkbox to sit vertically at the top or in the middle (like the switch component), a minor tweak we could decided upon when implementing ... but regardless.

[dstrukt]

Updates

[dennisreimann]

Shall we replace the box-shadow that the focused inputs currently have with the green border also?

How should this translate to dark mode?

[dstrukt]

Hopefully this should answer some questions .. would like to improve some of the :focused states as well, as you'll start to see in some of the mocks posted, but I'm going to take a look at the code changes you make so I can learn from that and submit some PRs as well, as this isn't the most exciting work I know :)

Have had to do accessibility stuff (I'm sure we're breaking a few rules there as well, intend to adjust some colors, but after we hook everything up) ... and it's even less fun.