Check If Current Page Uses Gutenberg or Classic Editor
If you’re themes like most themes, and you have to fix your main elements CSS to accommodate Gutenbergs edge-to-edge capabilities on gutenberg-only pages, it’s good to know which pages are actually using Gutenberg. The follow will add a CSS body class for Gutenberg pages.
Add conditions like
get_post_type() != 'post', etc., to accommodate your theme setup.