Skeuos is a GTK application theme inspired by the latest skeumorphic design trends, by embracing the bevels, drop-shadows, and gradients most modern themes actively avoid.
Closed! Completely my mistake, I didn't realize that setting an application theme would reset your shell theme. If anybody comes across this issue, please read this.
I'm not sure if regular Ubuntu/Gnome has this issue, or if it's just Pop!_OS.
Please see this video. Notice that Adwaita-dark does not have this issue.
Other things that are white with skeuos dark themes enabled: