This is an error in the file README_styles.css, which is to be copied into Site administration > Appearance > Additional HTML > Within HEAD (or other location appropriate for CSS), so this will need to be updated manually if the CSS was copied before the fix.
The fix for Moodle 4 (should also apply to Moodle 3.x): ab55753
This is an error in the file README_styles.css, which is to be copied into Site administration > Appearance > Additional HTML > Within HEAD (or other location appropriate for CSS), so this will need to be updated manually if the CSS was copied before the fix.
The fix for Moodle 4 (should also apply to Moodle 3.x): ab55753