body 
{
background-color: #efefef;   
background-image: url(https://img-blog.csdnimg.cn/20200718094952975.jpg?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQzNDc1MzM2,size_16,color_FFFFFF,t_70);   
background-repeat: no-repeat;   
background-attachment: fixed;   
background-position: center 0;   
background-size: cover;
opacity: 0.75;
}