Themes
Pinepods comes with 25 themes, light and dark. Pick one under Settings → Change Theme: click a theme's card and it applies straight away. Show N more expands the full list.
Your theme is saved to your account, so the web app, the desktop app and the mobile app all use the one you chose last. Changing it on the mobile app (Settings in the app) changes it everywhere too.
Themes you build yourself show up under My Themes in the same section. See Custom Theme Creator.