UPDATE: I FOUND THE SOLUTION! After checking out the github repo, it turns out that I installed the theme in ~/.config/gtk-4.0 with a bunch of CSS files and an "assets" folder (I honestly forgot I did that haha!) so after deleting those the theme has been removed! Looks like if I want to install another theme I have to put in new CSS files.

original post here:

I have earlier used a theme when I used GNOME (a forest green one), but have switched to KDE Plasma (which I have set to a purpleish catppuccin theme) for a while now. Interestingly, the theme I set to GNOME has persisted for certain GTK apps (even after a distro hop, it's stored in the home directory I presume?).

How would I go about changing the GTK theme to a different one that matches better with my KDE theme?

edit: It looks like some GTK apps respect the system theme while others retain my old theme I used with GNOME (like GNOME Calendar, Rnote, and Pinta)

I will try installing a theme with the GTK themes menu and report back.

edit 2: After changing the theme to a different one and restarting, no luck for apps like Rnote and Pinta. Maybe the themes option from that menu don't work on some GTK apps? (the preview mentioned GTK3, does the option not affect GTK4 apps maybe? I have no idea)