How to create custom card color in bases (with a css snippet probably?)

I have a bunch of to-do’s in bases card view, where I can visually keep track of them. Right now I have a simple cross, hourglass and checkmark below the image that shows if the to-do is ‘not started’, ‘in progress’ or ‘done’.

However, I would like the finished to-do’s to be more visually clear by changing the bases card to a different color when the status changes to ‘done’. Having a transparent overlay on the cover image would also be fine, as long as the image itself is still visible. I’m guessing this is possible with a custom css snippet, but I have no idea how to write the code for one and have not been able to find something similar online to help me get started.

This is an example of what I would like to have:

Can anyone help me out? Thanks in advance!