Try https://b.piefed.social/ instead! Log in with the same username and password as piefed.social.
It works best on a phone / tablet but on a desktop it’s fine too once you switch to compact mode.
It can be installed as a PWA.
There are also lots of themes you can try at https://piefed.social/user/settings. Here are some screenshots of them - https://join.piefed.social/screenshots/
That link should be “x.piefed.social”. ;)
EDIT
I’m confused about the Themes bit - did you mean that as in “there are other themes than the default one for regular PieFed, and that’s information that’s unrelated to b.piefed.social”?
FAKE-EDIT
PLEASE add the Ctrl+Enter shortcut to send comment/post!
The themes are indeed for the default Piefed UI