html
{
    background:url(https://files-cdn.cnblogs.com/files/lsqwq/2018110600636_KjMPc.bmp?t=1644636568) top center no-repeat #000;
    background-attachment: fixed;
    background-size:100%;
}
body
{
    background:none;

}

#home{
    opacity: 80%;
}

#top_nav{
    opacity: 0%;
}