Hello,
There is no option to set the size for tegs, Typography tab in the Theme Settings allows settings the sizes for titles. Besides, there are Advanced typography options.
You can change the font by means of Advanced typography option, which allows to choose the item from a drop-down or insert your custom CSS class. Please navigate to the Theme Settings > Typography > Advanced Typography.
Here is the documentation providing more detailed instructions: https://xtemos.com/docs/basel/advanced-typography-settings-2/
Best Regards