Steps to replicate the issue:

• Try to create a templateStyles sheet with list-style-type: 'X' or list-style: 'X'

What happens?
While saving, you get “Invalid or unsupported value for property list-style-type at line 3 character 19.”

What should have happened instead?
Sanitizer should let you save the page.

Other information:
Workaround: use inline style attribute (eventually with inherit keyword in templateStyles).