body {
    overflow: hidden;
    position: absolute;
    width: 100%;
    height: 100dvh;
}

div {
    position: absolute;
    top: 50%;
    left: 50%;
    width: 1em;
    height: 1em;
    margin: -.5em 0 0 -.5em;
    font-size: 20px;
    border-radius: 1em;
    background-color: currentColor;
}