Hi Vlad,
I assume you are talking about the bottom form that is part of the Vehica theme.
This plugin, as I feel it should, does not overwrite styling of a theme. It is up to the theme to give styling to form elements so you can have a consistent look on your website.
I looked at that form, but I don’t understand anything about how they do give styling to it. Since it is a commercial theme you have a right to support from the maintainers.
I wonder too how they think about form plugins and their styling :) I do hope the theme doesn’t just support their own form, but also any form plugin for WordPress.