body {
    margin: 0;
}
.main {
    position: fixed;
    top: 100px;
    left: 100px;
    width: 400px;
    height: 300px;
}
.main1 {
    position: fixed;
    top: 0;
    left: 0;
    width: 400px;
    height: 300px;
}
.main2 {
    position: fixed;
    top: 300px;
    left: 0;
    width: 400px;
    height: 300px;
}
.main3 {
    position: fixed;
    top: 0;
    left: 400px;
    width: 400px;
    height: 300px;
}
.main4 {
    position: fixed;
    top: 300px;
    left: 400px;
    width: 400px;
    height: 300px;
}
.mainScreen {
    width: 100%;
    height: 100%;
    background: #6fa;
}
.child1 {
    width: 100%;
    height: 100%;
    background: #f6a;
}
.child2 {
    width: 100%;
    height: 100%;
    background: #a6a;
}
.child3 {
     width: 100%;
     height: 100%;
     background: #eee;
 }