body 
{
    background-image: url(https://images.cnblogs.com/cnblogs_com/BlackJack-Tone/1110457/o_%e5%8d%97%e5%b1%b1%e5%8d%97%e4%b8%80.bmp
);
    background-repeat: no-repeat;
    background-attachment: fixed;
    width:100%;
    height:100%;
    background-size:100% 125%;
    opacity: 0.8;
    filter:alpha(opacity=80);
    background-position:center;
}