Once logged into the Live UI, in a browser, a menu is accessible. This can be found in two places depending on your screen size:
This enables navigation around the site as well as access to change the color scheme, enter Settings and log out.
By default the site will use the System color scheme, matching the users browser settings.
This allows you to change the site between Light color scheme and Dark color scheme depending on your preferences.
The color scheme of the site is user-specific, by default this will inherit the user's system setting.
You can control the colors used within each color scheme via the Appearance Settings.