What's happening is that the default skin (and many other things) are being tweaked as we go along here. So when that happens, it tends to screw with the code for the Stylish extension, creating things like the white boxes in the user info. The poster who created the dark scheme will have to update it as well, which will happen when they have time to do so.
Here are some other skins that can be taken for a testdrive in Stylish as well:
https://userstyles.org/styles/148942/bruins-light-grey (Basically same gold accents as the Pens)
https://userstyles.org/styles/148883/hfboards-dark-theme (Similar to the original posted in this thread)
If you do install multiple skins for the site, make sure to go into the Stylish options and make sure you only have one of them activated at a time, otherwise you're probably going to get some funky, unreadable results.