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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May I know which of your forms you wanted to edit or change the style?
In your Form Designer, you can edit the width and other layout settings of your form.
To access it you can navigate to the Designer from your Form Builder.
Inside your Form Designer, you can do a lot of things and that includes the width and other layouts. You can also inject a custom CSS code there.
I hope this helps. We'll wait for your response.