Thank you! Appreciate the help.
When I implement that code in full it seems to break the thumbnail scaling for some reason - as in the attached screenshot.
After messing around with it a bit it seems like the issue is caused by the third line -
width: 100% !important;
Changing that percentage doesn't help, but deleting the line completely seems to make it function as intended - as in the current active layout. No idea why that fixed it, but I'm happy with the result!
Thanks again!