Add utilities like mdUpper, lgUpper

[juliomuhlbauer]

I use a lot of mdDown, and lgDown. But there is not something in the opposite.

[segunadebayo]

mdUpper, and lgUpper sound like the current md and lg breakpoints.

[juliomuhlbauer]

Makes sense, it was not intuitive for me though. I thought that md was applying only to md screens, but makes sense because there is a mdToLg.
I think it would be more intuitive to use mdUpper instead.
Thanks!

[segunadebayo]

By design, you really shouldn't have to rely on *Down and *Up (proposed) if you use the mobile-first approach.

We won't be able to support this right away since there's an existing solution. I admit it might not be intuitive for you.