Captions let you read the words spoken in the audio portion of a video, TV show, or movie. To define how the captions appear in Windows and some Windows apps, you can select one of the predefined caption options or customize an option to better suit your needs.
Select (Start) > Settings > Accessibility > Captions.
In Caption style, expand the menu, select one of the predefined options, and see how it appears in the preview.
To customize the selected predefined option, select Edit and then modify the option details to your liking.