.box1 {
    width: 200px;
    height: 200px;
    background-color: rgb(255, 0, 0, 0.5);
    position: absolute;
    left: 100px;
    top: 100px;
    z-index: 100;
    opacity: 0.5;
}

.box2 {
    width: 200px;
    height: 200px;
    background-color: green;
    position: absolute;
    left: 150px;
    top: 150px;
    z-index: 50;
}

.box3 {
    width: 200px;
    height: 200px;
    background-color: blue;
    position: absolute;
    left: 200px;
    top: 200px;
}