body{
     background-image:url(https://images.cnblogs.com/cnblogs_com/yblue/1933083/o_210219005337zwq.jpg);
     background-attachment:fixed; //设置背景图像是否固定或者随着页面的其余部分滚动
}
#home{
     opacity:0.7; //0.0到1随便设置，越低越透明
}