This article guides you through creating a new theme that will be customizable in each experience and available globally. If you need an overview of the theme designer, this article here goes into more detail.

What to do

You can access the Theme Designer in two places, the availability of your new theme is determined by where it is created:

1. From the Dashboard area, click +.
2. Click Create Theme.
3. Enter a name for your theme, then click next >.
4. Choose a Foundation Theme to base your new theme on.
   Here you will see a selection of Themes that are available for you to use as base for your new theme.
5. When prompted to Enable Customization? It's recommended that you select the box, if you do not, then you will not be able to customize the theme in each activation that uses it, this of course, may be entirely intentional. 
6. To finish, click + Create.

Flex or Scaffold may be the best options for a new customisable Theme, as these offer more of a blank canvas to start from.