div{
    width: 100px;
    height: 800px;
    background-color: aqua;
    margin-right: 2px;
    margin-top: 200px;
    float: left;
}

.bloc2 {
    position: fixed;
    height: 1000px;
    margin-left: 150px;
    opacity: 0.5;
    margin-top: 1px;
}

.bloc3{
    margin-left: 200px;
}