Font size cannot be edited in blog post in the full post layout

I'm trying to change the font size in my blog posts (in the full post layout) and I don't seem to have the option. My steps:

In Wix website editor, click on the blog post

Select 'Settings'

In the pop up window click 'Design'

Then click 'Posts'

Scroll to the bottom where there are the tabs 'All posts feed' and 'Category Pages'

Both of those tabs should have 'Title Font Size', 'Description Font Size', and 'Border Width' listed below (according to the wix help center page in the screen shot below)

However that isn't showing up for me--only 'Border Width' (screen shot of what I am seeing below)

The result being the font is just some default size and is larger than I would like

Is this changeable? What am I missing?

Thank you.