Edit: I didn't adequately research this question before posting it, so the behavior I'm describing is much older than I realized. The issue I was observing comes from elsewhere. Leaving the original question here for context.
add_editor_style copies the styles of the body {} selector from the specified stylesheet into the class selector .editor-styles-wrapper {}. This isn't well-documented, as far as I can tell, other than in a comment in the documentation.
Since upgrading to 6.3 (or possibly earlier), I notice that the styles on html {} are also being copied to .editor-styles-wrapper {}.
So if you load a file like editor-styles.css that contains the following declarations:
html { font-size: 100%; } body { font-size: 1.2rem; } WordPress will inject these styles into the editor as:
.editor-styles-wrapper { font-size: 100%; } .editor-styles-wrapper { font-size: 1.2rem; } (Previously, the html {} styles would have just been dropped.)
Is this intentional? Is it documented anywhere? This has led to some slight breakages in my editor styles.
add_editor_styleare no longer prependingeditor-styles-wrapperwhich has broken all my block editor css!