Issue Summary

With Firefox, if you hover your mouse over a card with a dark theme, you'll see a problem in the UI.

The white lines between the blue and black shouldn't be there.

Steps to Reproduce

1. With firefox access a board with cards
2. Make sure you have dark theme enabled
3. Hover your mouse over a card and you'll see the problem.

Expected Results

Smooth lines and no white around the blue line. 

Actual Results

A white line in some parts around the blue line.

Workaround

None