I'm wrong. content:normal doesn't work. And if you try to edit the template file and escape characters manually the error message is: Invalid property value: contentSo should be the "content" rule causing the problem

I think the problem with the content property is the ' " ' character.Remember that the custom css is going to be reflected on the json file associated with that template, and ".className {content: " ";} would break the json file. A possible solution ...