Looking to customize your form’s theme with CSS? Use Custom CSS instead.
How to use the HTML field
The HTML field lets you add a custom HTML block to any part of your form, including custom CSS and custom Javascript code.Note: This feature is available on the Business and Enterprise plans. Learn more about our pricing plans and advanced features here.
HTML
field. Then, click the settings icon
to open the right-hand panel so you can Edit HTML
and Edit CSS
.

Custom scripts and iframes
The HTML block also supports scripts and iFrames. To support these, enable theAllow scripts and iFrames
toggle in the right-hand panel.
Important: Scripts only run your published form, not in preview mode or in the editor. Go to the live mode of your form to test it out.
Furthermore, you will need to connect a custom domain for the scripts to run.
Note: Currently, the HTML block is not easily suitable for adding form inputs. For example, it can’t be used to create custom input fields.