html,
body {
    position: fixed;
    top: 0px;
    left: 0px;
    height: 100%;
    width: 100%;
    background: rgba(255,255,255,0);
    background: radial-gradient( at center, rgba(255,255,255,0), rgba(255,255,255,0));
}

#particles-js {
    background-size: cover;
    background-position: 50% 50%;
    background-repeat: no-repeat;
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
}