Hello,

Try this code CSS:

[type=submit].btn-color-black{
    padding: 12px 20px;
    background-color: #bea163;
    display: inline-block;
    position: relative;
    font-weight: 600;
    text-align: center;
    text-transform: uppercase;
    letter-spacing: .3px;
    border-radius: 0;
    border-width: 0;
    border-style: solid;
    border-color: transparent;
    outline: 0;
    -webkit-box-shadow: none;
    box-shadow: none;
    text-shadow: none;
    text-decoration: none;
    vertical-align: middle;
    cursor: pointer;
    -webkit-transition: color .25s ease,background-color .25s ease,border-color .25s ease,box-shadow .25s ease,opacity .25s ease;
    -webkit-transition: color .25s ease,background-color .25s ease,border-color .25s ease,opacity .25s ease,-webkit-box-shadow .25s ease;
    transition: color .25s ease,background-color .25s ease,border-color .25s ease,opacity .25s ease,-webkit-box-shadow .25s ease;
    transition: color .25s ease,background-color .25s ease,border-color .25s ease,box-shadow .25s ease,opacity .25s ease;
    transition: color .25s ease,background-color .25s ease,border-color .25s ease,box-shadow .25s ease,opacity .25s ease,-webkit-box-shadow .25s ease;
}

Add it to the Theme Settings > Custom CSS

Best Regards