The guide explain how to use the UI assets, but don't explain where it is suppose to be set. For exemple, Photoshop and Illustrator have specific folders where goes it presets. I came to the forum looking for the same answer since I didn't found any folder for Affinity, only to some Moderator brush it off as we were idiots. Thank you for nothing. :P And a real thank you, v_kyr, for the patience to explain.