$img1: 'http://pic7.photophoto.cn/20080407/0034034859692813_b.jpg';

$img2: 'http://up.enterdesk.com/edpic_source/21/00/00/210000f8e772d7fc0758e67ae4b48807.jpg';

$img3: 'https://images.unsplash.com/photo-1440688807730-73e4e2169fb8?dpr=1&auto=format&fit=crop&w=1500&h=1001&q=80&cs=tinysrgb&crop=';

section {
    height: 100vh;
    background: rgba(0, 0, 0, .7);
    color: #fff;
    line-height: 100vh;
    text-align: center;
    font-size: 20vh;
}

.g-img1 {
    background-image: url($img1);
    background-attachment: fixed;
    background-size: cover;
    background-position: center center;
}

.g-img2 {
    background-image: url($img2);
    background-attachment: fixed;
    background-size: cover;
    background-position: center center;
}

.g-img3 {
    background-image: url($img3);
    background-attachment: fixed;
    background-size: cover;
    background-position: center center;
}