Preferences - there

Access these settings by clicking your avatar at the bottom left of the sidebar, selecting Manage account, then opening the Preferences tab.

Appearance

Select the display theme:

Option	Behaviour
Light	Always use the light theme
Dark	Always use the dark theme
System	Follow your operating system setting automatically

The preference is saved to your account and applies across all devices where you are signed in.

To quickly change your appearance, click your avatar at the bottom left of the sidebar and select Appearance.