Menu UI tweaks

[TanayB11]

Change the learn/quiz/srs Front option menu to something more palatable than a slider. The slider feels unnatural for this purpose, but I'm still thinking about it. This page Options before starting a review feels a bit sparse. Play with the sizing and spacing of these items.

Additionally, add padding and filling around each button. This will probably be done during the UI overhaul, but it's still a good idea to put padding on some of the buttons at least to get a feel for the design and layout.