div#main {
    height: 300px;
    width: 300px;
    position: absolute;
    margin: 0 auto;
    transform: translate(-50%, -50%);
    top: 50%;
    left: 50%;
}
div.circle {
    position: absolute;
    width: 85px;
    height: 85px;
    border: 2px solid black;
    border-radius: 50%;
}
body {
    margin: 0 auto;
}