I'm sorry to hear that! I just posted a listing in my account and was able to select a category and style (adjust the font size and style) my item description and listing template without any issues. Are you still facing this issue when creating a listing? If you are I'd recommend you reach out to our Customer Support Team
as they'll be able to take a closer look at your account and help debug the issue.
Again I'm sorry about the inconvenience you've faced, but let me know if it's still an issue.