Customizer changes are not applying in CKEditor environmentr

Problem/Motivation

Pretty much issue title, when a CSS variable value is changed in theme settings, it's new value is not available on CKEditor environment.

Steps to reproduce

1. Go to /admin/appearance/css-variables-customizer/theme_name
2. Override the h2 font-size
3. Go to the create/edit form of an entity with a formatted text field
4. Add some text and make it h2 using the CKEditor toolbar
5. Check that font-size is override its not applying