Customize the Appearance in Microsoft Teams Free

Open Microsoft Teams Free.

Select Settings and more near your profile picture.

Select  Settings .

Select Appearance ⁠.⁠

Under Theme , from the drop-down you can select:

1.  Follow operating system theme, Light, Dark, or High Contrast.
2. You can also turn Always use dark theme for meetings and calls on or off.

Your theme will change to your selection.