xxxxxxxxxx<html><head><meta name="viewport" content="width=device-width, initial-scale=1.0"><style> /* For width smaller than 400px: */ body { background-repeat: no-repeat; background-image: url('/statics/images/course/img_smallflower.jpg'); } /* For width 400px and larger: */ @media only screen and (min-width: 400px) { body { background-image: url('/statics/images/course/img_flowers.jpg'); } }</style></head><body> <p style="margin-top:360px;">调整浏览器宽度，背景图片在小于 400 px 时将改变。</p></body></html>