.parent-element > * {
    width: 100%;
    position: relative;
    z-index: 1;
}
.child-element {
    box-shadow: 0 3px 6px 0 rgba(0, 0, 0, 0.5);
    min-height: 100vh;
    background-color: #fff;
}
.element-1 {
}
.element-2 {
}
.element-3 {
}
.element-4 {
}
.curtain-fixed {
    position: fixed;
    top: 0;
    z-index: 0;
}