The crop on some thumbnails is just bad. So, rather than having them cropped, this style resizes the image.
When installed as a script, it does show on all sites as active, but it shouldn't affect any other site. It's originally CSS, and when GreasyFork converts to JS, it does not do the @match properly. I let it offer the option because it seems to work fine. If it does not, please let me know.
This script seems to apply to all websites, not just DeviantArt. So this is pretty much a universal script.