Welcome to Subeta! we have a great artist community here, so hope you like it here!

Bookmarks: Personal > User Dashboard > Bookmarks (The dashboard page may have a small lag the first time you load it, because it also retrieves the information for your sP ranking)

I'm afraid I use the desktop version when I'm on my phone so I'm not too sure about it, but I do think there might only be the one theme. Someone else might correct me u_u;

Useful Links:

What to do on Subeta? Useful general information for newbies Finding friends (Chit Chat) SubetaLodge (Offsite item database, pet colours etc.)
FAQ