You would have to overwrite the Customizer settings using CSS in order to use EMs currently. It’s something I’m playing with when it comes to the Customizer.
I dont have problems with browser: i overwrite CSS with “!important” Its OK
example: body, button, input, select, textarea { font-size: 0.9em!important; }
——
but “online accessibility validator” find error in source code
body, button, input, select, textarea { font-family: “Open Sans”, sans-serif; Marca font-size: 14px; }
this “source code” with “font-size:14px” from theme
No need to use !important, just make sure your CSS loads after the theme CSS (use a child theme or a plugin like Simple CSS).
Removing all CSS with px would be very difficult I’m afraid. However, just because the validator finds the px and spits out an error (false positive) doesn’t mean it will be an issue with accessibility, especially if you’ve added ems.