mod extroforms uses two CSS Files:
the first file you can edit via Backend is: your_Joomla_root_directory/components/com_extroforms/css/extroforms-[form ID of the used Form].css. That file was generated by each Form.
The second one you will find at: your_Joomla_root_directroy/modules/mod_extroforms/mod_extroforms.css If you edit these two file you can Change the CSS Layout.
I hope my answer was helpful to you.
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