.maindiv{
    text-align: center;
    background-color: gray;
    padding: 20px;
}
.maindiv::after{  /* this is clearfix */
    display: block;
    clear: both;
    content: "";
}
.div1{
    background-color: red;
    float: left;
    width: 10vw;
}
.div2{
    background-color: rgb(105, 246, 241);
    float: right;
    width: 10vw;
}
.div3{
    background-color: rgb(148, 0, 143);
    float: right;
    display: none;
    width: 10vw;
}
.div4{
    text-align: center;
    background-color: green;
}
.box{
    padding-bottom: 150px;
    color:white;
}