I want to know if all GP Sites are compatible with Gutenberg Block Editor.
I use the Marketer Site on my Page and I sinf some Issues, where it seems that it is not compatible. For example, when using a quote, the the color options for the quote has no effect.
Gutenberg has an optional stylesheet that is sometimes required for some of their more opinionated styles. You can try adding this snippet to see if it fixes the issue:
It loads wp-block-library-theme-css on your <head> which is another file within WP core.
And if so, is this not bad for sitespeed to load another css file?
You can check how much of an effect it does to your site on page test websites (GTMetrix, Google PSI, Webpagetest.org). But it shouldn’t have that much of an effect especially of your site is well-optimized.