Visually group cards on a dashboard

**Is your feature request related to a problem? Please describe.**
In a dashboard with multiple charts, want to be able to visually group them together (such as with a border around the cards or a the same background color behind the cards in the same group). Gives a little more context to the user on the data presented.

**Describe the solution you'd like**
something like this 

**Describe alternatives you've considered**
Leaving space on the dashboard between the different charts, have users infer the groups.

**How important is this feature to you?**
would be nice, visually

The issue names no files, tests, or entry points. Start by locating the dashboard card layout and styling entry points, then determine how grouped cards should be represented and configured. Done means dashboard users can visually distinguish related cards with a border or shared background, with the behavior covered by the relevant tests.

Written by the indexing model from the issue text.