CSS Error with WP 4.8

After updating to WP 4.8, I started getting this message:

Failed to load content css: http://www.mydomain.com/wp-includes/js/tinymce/skins/wordpress/wp-content.css?ver=4.8

After researching, it appears that it is a compatibility issue with your theme. Just FYI. I’m deactivating (even though I love your theme) until it can be fixed.