What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
I believe you are referring to the headings. The "Shrink" option is greyed out because the headings should occupy the whole horizontal space. You cannot use "Shrink" in headings.
You can use the "Text" tool and then adjust or format the font size on how you want it to be. After that, you can just right click the field and then "Shrink" it.
If you double click the text field, the text editor will come up.
Let us know if you need any help. Thank you.