I know this has been brought up in the past, but so far none of the solutions have worked for me.
I’ve been using the Edit Layer feature to ensure the entries on the layer all follow the same format. To do this, I’m editing the description using DIV tags. This has worked perfectly since October of 2024.
Looking at the issues on the umap github, I think this recent report may be the same issue. It is not described entirely clearly, but I think both issues relate to CSS being displayed as literal text instead of intepreted as styling.
If you have or are willing to set up a Github account, it might be worth chiming in on that issue with more details, including a URL as requested by a maintainer.