body,
html {
    width: 100%;
    height: 100%;
    min-height: 100%;
    padding: 0;
    margin: 0;
    background: #eee;
    color: #fff;
}
h1 {
    font-size: 2rem;
    margin: 0 0 15px;
}
a {
    color: #fff;
}
a:hover {
    text-decoration: none;
}
.main-wrap {
    width: 100%;
    height: 100%;
    }
    .main {
        text-align: center;
        vertical-align: middle;
    }
    label {
        font-weight: bold;
    }
    .main-content {
        width: 400px;
        max-width: 100%;
        padding: 40px 20px;
        margin: auto;
        background-color: rgba(0, 0, 0, 0.8);
        -webkit-box-shadow: 0 0 100px 50px #000;
                box-shadow: 0 0 100px 50px #000;
    }

body {
    background: url(../images/bg-576x360.jpg) 50% 50% no-repeat;
    /*-webkit-background-size: 100%;*/
    /*background-size: 100%;*/
}
@media (min-width: 576px) {
    body {
        background-image: url(../images/bg-800x500.jpg);
    }
}
@media (min-width: 768px) {
    body {
        background-image: url(../images/bg-1000x625.jpg);
    }
}
@media (min-width: 992px) {
    body {
        background-image: url(../images/bg-1280x800.jpg);
    }
}
@media (min-width: 1200px) {
    body {
        background-image: url(../images/bg-1600x1000.jpg);
    }
}
@media (min-width: 1600px) {
    body {
        background-image: url(../images/bg-1920x1200.jpg);
    }
}