Mailchimp horizontal form on mobile

hi – thank you so much for the excellent theme. I wanted to make my mailchimp form into a horizontal layout. Using the code I found in the forum, it works pretty well on desktop, but for mobile, the elements should stack instead of maintaining their horizontal layout. Please take a look on mobile to see the problem.

Here is the code I found and am using in quick css:

#top.home .avia-mailchimp-form p.first_form {
float: left;
width: 30%;
margin-right: 1.3333334%;
clear: none !important;
}

#top.home .avia-mailchimp-form p.first_form.av-last-visible-form-element {
margin-right: 0 !important;
}

Site url found below.
Thank you!
Doug