Add list of global CSS variables

[camwiegert]

We need to add a list of all global variables (e.g. --ion-statusbar-padding) to this page.

[brandyscarney]

I am thinking we should just manually document this. Thoughts?

[camwiegert]

@brandyscarney Agreed. I think that'll be simplest. Probably just add a table at the bottom of the page and link to it from the "Global Variables" section.

[brandyscarney]

Closed by bb35500

We can iterate on this if desired.