.webform-button--submit {
    position: absolute;
    top: 50%;
    left: 50%;
    text-align: center;
    margin: 0;
    margin-bottom: -15px;
    padding: 0;
    background: #ccc;
    -webkit-transform: translate(-50%,0%);
    -ms-transform: translate(-50%,0%);
        transform: translate(-50%,0%);
}

.col-centered{
    float: none;
    margin: 0 auto;
}