Update spacing to match 8-pt grid values shown in Figma

[angela-tran]

This ticket is for updating the spacing in MobiMart so that it matches the 8-pt grid that design uses for their Figma screens.

Additional context

Yes, this does follow the 8-pt grid. Whenever I create new designs for mobimart or calitp.org, I automatically update with that design framework. I know we never discussed that explicitly for the homepage dev work though—I'll do a better job noting that when we're scoping in the future. If we can create a new ticket for updating the spacing in backlog that would be great

Originally posted by @segacy1 in #489 (comment)

[angela-tran]

We don't know exactly how much there is on MobiMart to update over to 8-pt grid (it could be a lot). And MobiMart uses Sass, so it works differently from what we're used to in Benefits.

A dev should go through and see how much there is to update.