图片自适应居中显示

html

<div class="box">
    <img src="img.png" />
</div>

css

.box{
    width: 500px;
    height:500px;
    position: relative;
    border: 1px solid #eee;
}
.box img{
    position: absolute;
    left: 0;
    top: 0;
    right: 0;
    bottom: 0;
    max-width: 100%;
    max-height: 100%;
    margin: auto;
}