The line to import catppuccin Stylus is as follows:
@import url("https://catppuccin.github.io/discord/dist/catppuccin-" + theme + "-" + accent + ".theme.css") */
Because the settings for the style has the first letters capitalised ("Macchiato" and "Flamingo" in my case), it fails to load the theme. However, if I manually change the url to "https://catppuccin.github.io/discord/dist/catppuccin-" +"macchiato"+ "-" +"flamingo"+ ".theme.css" (or just make it 1 string), the theme loads just fine.
I see that there are var selection above, but there must be something wrong with it, so I don't know.