The Goog seems to be in the process of migrating chat.google.com functionality into Gmail. The tricky part is that while the classes they use are generally the same, making the styles work on both "platforms" can get a little messy. This UserCSS reflects that journey. There are classes that overwrite each other, a few blank rules, and way to many undocumented style rules (the class names aren't helpful at all).

Please feel free to contribute if you like. Since there are still several places that need to be styled better, I plan to revisit as time permits. If you set the style to auto-update when you install it, you will get the changes.