Where is my CSS from custom CSS section?

Since the 2.0.4 update, we've deprecated custom CSS section under the Ultimate member -> Settings -> Appearance tab. Please use WordPress built it customizer in Appearance -> Customize and Additional CSS.

The Ultimate member 2.0.4 will still include your legacy custom CSS which you can find on your server

/wp-content/uploads/ultimatemember/um_old_settings.css