Hi,

Please try add more this code to Customize > Custom CSS to do that:

#respond textarea,
#respond input[type="text"],
#respond input[type="email"]{ 
    border-color: #a67c52;
}
#respond .form-submit input.submit{
    color: #fff !important;
    background-color: #a67c52 !important;
}

Best Regards,

PenciDesign