Style the filter panel

[asbates]

I think there's some room for improvement for the filter panel styling. Well panel's are a bit outdated, hard coding colors (blues and red) are probably not a great idea, to start with.

We should really think about restyling across the whole app though because a lot of the same styling is used and just having the filter panel different will probably look weird.

[donyunardi]

We're now proceeding with the restyle here:
insightsengineering/teal#1289

Closing.