Your app theme changes what you see. Your profile theme changes your profile. A group theme changes that group for people who view it.

Your app theme is your personal interface style. Change it in Settings when you want Bliish to look different for you while you browse.

Your profile theme is the style visitors see on your profile. Use it to make your own profile feel distinct without changing everyone else's app theme.

A group theme belongs to a group. People who view that group can see the group's style, so it works best when it matches the group's identity or topic.