Hi there,
the form is controlled by the Mailchimp MC4WP plugin it has its owns settings in the dashboard.
Its styles are add using Customizer > Additional CSS. Its code is this:
/* mailchimp form styling */
.mc4wp-form input[type="email"] {
background-color: #f5f3f2;
line-height: 34px;
margin-bottom: 10px;
width: 300px;
border: none;
border-radius: 2px;
font-size: 15px;
}
@media (max-width: 767px) {
.mc4wp-form input[type="email"] {
width: 100%;
margin-bottom: 10px;
}
}
.mc4wp-form input[type=submit] {
color: #ffffff;
line-height: 34px;
font-size: 16px;
letter-spacing: 1px;
width: 150px;
border: none;
border-radius: 2px;
-webkit-transition: all 500ms ease-in-out;
transition: all 500ms ease-in-out;
}
@media (max-width: 767px) {
.mc4wp-form input[type="submit"] {
width: 100%;
}
}
Let us know if theres anything specific you want to change.