body {
    margin: 0;
    padding: 0;
    position: relative;
    height: 100dvh;
    overflow: hidden;
}

.simulation {
    height: 100%;
    background-color: #999999;
    z-index: -2;
}

.particle {
    width: var(--diameter);
    height: var(--diameter);
    background-color: black;
    position: absolute;
    transform: translate(-50%, -50%);
    border-radius: 50%;
    z-index: 0;
}