the new wordpress Version brought as the ability to switch between sites and templates within the editor when using the website-editor.
However, when editing a Site inside the website-editor it seems that it doesn’t regenerate the CSS for that site.
When I hit save all the styles appear inside the editor (also if i open the site editor the “normal” way), but i have to hit update to trigger the CSS Regeneration when editing the site accessed via the “Pages” menu.
I can confirm that there is currently an issue with the CSS file generation for the edited post/page when inside the Site Editor.
We’ll make sure to have this fixed in the next release.
As for the Post Content block not being editable, as @Marius pointed out, this is currently out of our hands as content modification is being blocked by Gutenberg without any hook allowing blocks other than “core/content” to modify the loaded post/page.
This will hopefully be possible in the next WordPress release.