header.masthead {
    position: relative;
    /*height: 40vh;*/
    height: 60vh;
    background-color: #fff;
    background: url("/img/slider/slider.jpg") no-repeat center center;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
    padding-top: 8rem;
    padding-bottom: 8rem;
}

header.masthead .overlay{position:absolute;background-color:#212529;height:100%;width:100%;top:0;left:0;opacity:.3}

@media (min-width:768px) {
    header.masthead {
        padding-top: 12rem;
        padding-bottom: 12rem;
    }
    header.masthead h3 {
        font-size: 2rem;
    }
}