How to reposition submit button in form

Site URL: https://magnolia-shark-g9jd.squarespace.com/

Hi all, 

I'm looking to position the submit button in the screenshot on the right of the form field instead of below it. 

URL: https://magnolia-shark-g9jd.squarespace.com/

Site password is: fiossftw

Template is Brine

Add to Home > Design > Custom CSS

@media screen and (min-width:641px) {
.newsletter-form-body {
    display: flex;
}
}

Thanks!