css-图片左右上下居中自适应大小

html

<a><img src="images/share/PHOTO_4.jpg" alt="埔里之春"></a>
<a><img src="images/share/PHOTO_4.jpg" alt="埔里之春"></a>
<a><img src="images/share/PHOTO_4.jpg" alt="埔里之春"></a>

css

a{
    display: block;
    overflow: hidden;
    padding-top: 66.75%;
    position: relative;
    border: 1px solid rgba(221, 221, 221, 0.3);
    margin-bottom: 20px;  
}
img{
    position: absolute;
    display: block;
    max-width: 100%;
    max-height: 100%;
    top: 0px;
    left: 0px;
    right: 0px;
    bottom: 0px;
    margin: auto;
}