typography

Is your feature request related to a problem? Please describe.
I don't think Theme UI should be opinionated on which SVGs should be used for the Radio & CheckBox components

Describe the solution you'd like
Probably an additional prop called customIcon maybe... based on which we could conditionally render the passed SVG icon otherwise we use the default icons?

**Describe alter

Hi,

I never used your lib yet, but very interested to (as I was starting to do a similar thing).
One thing I noticed is that I don't see dark colors (eg: iOS Colors have light & dark values, which are different, same for grey, see https://developer.apple.com/design/human-interface-guidelines/ios/visual-design/color/)

Is there any plan to handle that? Might be a bit breaking change for color

We can allocate those two in one vector allocation for all upon first non-nullptr setter. That would shrink hb_font_funcs_t by over 50%. Saves 33 pointers!