HTML 结构

<div id="small_gal">
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
    <div><img src="images1.jpg" /></div>
</div>

图像有阴影，所以border不是解决方案，因为它会在图像之外

边框有过渡，在 FF 上运行流畅，但在 chrome 或其他浏览器中运行不佳

这是我使用过的代码

#small_gal div:hover{cursor: pointer;}
#small_gal div:after {
    content: '';
    position: absolute;
    width: 112px;
    height: 81px;
    border: 3px solid #e27501;
    left: 9px; top: 9px;
    z-index: 9;

    opacity: 0;
    -webkit-transition: opacity 0.5s ease-in-out;
    -moz-transition: opacity 0.5s ease-in-out;
    -o-transition: opacity 0.5s ease-in-out;
    -ms-transition: opacity 0.5s ease-in-out;
    transition: opacity 0.5s ease-in-out;
}
#small_gal div:hover:after {
    opacity: 1;
}

Note:

#small_gal

只是容器 每个图像都包含在 div 中，因此我们可以实现 :after

Firefox 4+ 是唯一支持伪元素转换的浏览器，例如:before and :after.

Source: http://css-tricks.com/13555-transitions-and-animations-on-css- generated-content/ http://css-tricks.com/13555-transitions-and-animations-on-css-generated-content/