Change how the TYPO3 backend looks and behaves 

Customize the look, feel, and navigation behavior of your backend. These settings only change your own backend, not what other editors see.

• Color scheme: Choose Light mode, Dark mode or Auto detect, which follows the setting of your operating system.
• Theme: Choose one of the backend themes.
• Start up in the following module: Select the module you see when you log into the backend, for example Dashboard, Content > Layout or Media.
• Format of window title in backend: Set the text of the browser tab, for example whether the page title or the site name comes first.
• First day of week in calendar popups: Set whether calendars in date pickers start on Sunday or Monday.

Backend themes 

A theme changes the look of the backend. It does not change where things are or what you can do.