Make Fonts Available to Subthemes

Question

I have a Magento 2.3.3 instance that has many sites. We have purchased a theme, created a common subtheme that will be used as a parent theme for all sites.

To illustate:

1. purchased_subtheme (parent Luma)
   • common_subtheme (parent purchased_subtheme)
   • site_1_subtheme (parent common_subtheme)
   • site_2_subtheme (parent common_subtheme)
   • site_3_subtheme (parent common_subtheme)

We are using a custom font for all themes. How so you add the font to the common_subtheme so it inherits to all the site themes?