Increase toggle hit region

[surma]

I realized that I sometimes try to hit the toggle on mobile and I tap the region between the bottom bar border and the toggle and then nothing happens. It can be frustrating if you have sausage-y fingers like me.

I increased label to span the entire height of the bottom bar.

@jakearchibald PTAL if you agree with the way I achieved that.

I also switched the label to flexbox, because the absolute positioning seems unnecessary?

I also fixed text highlighting on Safari and older FF.

[jakearchibald]

See how the toggle isn't quite centered with the tiles above

[surma]

@jakearchibald Brought back the absolute positioning. PTAL.