You change the font size before you enter the name and change the font size back to default after you finish. The default size is 14.
Actually there seems to be an issue.
We expect that if the focus is in the label then only that specific field will be affected by the new font size. If you add a new field it will not be use this new font size.
Field with focus in the label :
Onthe other hand if the field is selected but the focus is no in the label then the global form's font size is changed to the new value. If you add a new field it will use this new font size.
Field without focus in the label :
I will log a bug on our side and get this fixed in a future release. Sorry for the inconveniences.