子比背景图优化代码

/***日间主题模式***/
body {
    background-image: url("https://blog.zmkj.website/api/suijibeijingtu");
    background-position-x: center;
    background-position-y: center;
    background-repeat: no-repeat;
    background-attachment: fixed;
    background-size: cover;
}
/***夜间主题模式***/
.dark-theme {
    background-position-x: center;
    background-position-y: center;
    background-repeat: no-repeat;
    background-attachment: fixed;
    background-image: url("https://blog.zmkj.website/api/suijibeijingtu");
    background-size: cover;
}

把代码复制粘贴到站点后台→全局功能→自定义代码里面的css里面就行啦