Css updates

@mlettini I'm looking for your +1 on this

@kenearley @stof @koenpunt @starzonmyarmz you guys should be aware of the change

This does two things:

- Changes the style of optgroups to be black. They look better, are easier to read and more closely match default `select` styles this way
- Change the specificity of our input styling. This should help with some of the "Bootstrap styles are off"-type issues we've been seeing a lot of (like #1263)

Pretty low-risk.