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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You can use injected CSS code like this
border: medium solid black;
to add border around your form.
Follow this user guide on -How-to-Inject-Custom-CSS-Codes
Check this demo form http://www.jotform.me/form/41516688940463
Hope this help. Inform us if you need more assistance.