.middlebox{
    display: -webkit-box;
    display: -ms-flexbox;
    display: flex;
    height: 70%;
    -webkit-box-align: center;
    -ms-flex-align: center;
    align-items: center;
    -webkit-box-pack: center;
    -ms-flex-pack: center;
    justify-content: center;
 }