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the best way I find to do this , use the html tool for your heading you have quite a lot of controls in there
There are two possible way to change the font size of form's heading.
1. It can be changed through the form toolbar. To do this you need to select the heading field of your form and then change the size by selecting one of the sizes from Default, Large and Small.
2. Another option is to inject the custom css to alter the look of the headings.
Please check the below mentioned thread where similar question is already answered: https://www.jotform.com/answers/89482-How-can-I-change-the-font-color-size-of-the-heading
Hope this helps.
Use this custom css and inject into your form in addition to my colleague's response.
font-size: 22px !important;
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