如何设置html中的背景图片（全屏显示，且不拉伸）

1 <style>
2 body{background-image:url(https://uploadbeta.com/api/pictures/random/?key=BingEverydayWallpaperPicture);

3 background-size:cover;background-attachment: fixed;
4 background-repeat:no-repeat;background-position:center } </style>