Thread:Andrewds1021/@comment-39340968-20200121213010/@comment-9605025-20200129175928

Create images offline then upload using Special:Upload instead of Special:AchievementsCustomize. However, this would require you to custom make the entire badge. In contrast, using Special:AchievementsCustomize requires only the picture you want featured on the badge.

There doesn't seem to be a CSS solution.