Keynote

Create and manage Keynote themes on Mac
If you add or edit a presentation’s slide layouts, you can save those changes as a theme to use again in other slideshows. Creating your own theme can be as simple as adding your company logo to an existing theme, or you can design a completely new theme. To learn more about creating and editing slide layouts, see Add and edit slide layouts.
You can add your custom themes to the theme chooser, save them as a file to share with others, and use them in Keynote on your Mac, iPhone, or iPad. Custom themes that you create on your Mac are grouped in the My Themes category of the theme chooser and are shared across all your devices.