To customize closed captions on an iPhone or iPad:
- On your iPhone or iPad, go to Settings menu.
- On the main Settings page, select Accessibility.
- Under Hearing, select Subtitles & Captioning.
- From here, you can toggle on the default closed captioning mode or change the Style.
- Select Style. Certain default customizations are available and can be selected, or you can also select Create New Style.
- Once finished making your changes, select Save in the upper right hand corner to return to the Caption Style page.
- Select your new custom style from the selections.
- Your customization is now enabled and will continue to display until changed using the steps above.
For more caption help, please visit Apple's caption user guide.