If the?max-width?property is set to 100%, the image will scale down if it has to, but never scale up to be larger than its original size:
img?{
??? max-width:?100%;
??? height:?auto;
}
?
来自： https://www.w3schools.com/css/css_rwd_images.asp
?
原文：http://www.cnblogs.com/time-is-life/p/7279321.html