This is what we have; I styled side-by-side for name & email for desktop, and 100% wide for mobile:
<p class="name-email-desktop"><label>[text* customer-name placeholder "Name"]</label><label>[email* customer-email placeholder "Email"]</label></p>
<p class="name-email-mobile"><label>[text* customer-name placeholder "Name"]</label></p>
<p class="name-email-mobile"><label>[email* customer-email placeholder "Email"]</label></p>
<label>[textarea customer-message placeholder "Message"]</label>
[submit "Submit"]