#square {
    width: 100px;
    height: 100px;
    background-color: red;
    position: absolute;
    top: 250px;
}

#circle {
    width: 100px;
    height: 100px;
    border-radius:100px;
    background-color: blue;
    position: absolute;
    top: 250px;
}

#triangle {
    width: 0;
    height: 0;
    top: 350px;
    border-left: 50px solid transparent;
    border-right: 50px solid transparent;
    border-top: 100px solid green;
}