关键是要有一个带有position: relative的块元素,然后是带有position: absolute的内部元素:
http://jsfiddle.net/coma/FeVsr/12/
HTML
<div class="news">
    <a href="#" class="boxing" style="background-image:url(https://si0.twimg.com/profile_images/3162594037/e232a8ce35fe8ce856e4a52a16141f20.jpeg);">
        <div class="summary">...</div>
        <div class="content">...</div>
    </a>
    <a href="#" style="background-image:url(https://si0.twimg.com/profile_images/3162594037/e232a8ce35fe8ce856e4a52a16141f20.jpeg);">
        <div class="summary">...</div>
        <div class="content">...</div>
    </a>
</div>
CSS
body {
    font-family: Arial, Helvetica, sans-serif;
}
div.news {
    padding: 10px;
    background: #eee;
}
div.news:after {
    content: "";
    display: block;
    clear: both;
}
div.news > a {
    display: block;
    float: left;
    width: 200px;
    border: 5px solid #fff;
    margin: 0 8px 8px 0;
    box-shadow: 0 0 3px rgba(0, 0, 0, .5);
    position: relative;
    background: #009BFF none no-repeat top;
    background-size: cover;
    font-size: 12px;
    text-decoration: none;
    color: #fff;
}
div.news > a > div.summary {
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 50px;
    padding: 5px;
    overflow: hidden;
    background-color: rgba(0, 0, 0, .7);
    line-height: 1.4em;
}
div.news > a > div.content {
    min-height: 200px;
    position: relative;
    opacity: 0;
    background-color: inherit;
    transition: opacity .5s;
    padding: 25px 5px 5px 5px;
    z-index: 1;
    font-size: 13px;
    line-height: 1.4em;
}
div.news > a:hover > div.content {
    opacity: 1;
}
div.news > a:before {
    content: "news";
    display: block;
    padding: 3px;
    background-color: inherit;
    position: absolute;
    top: 0;
    left: 0;
    text-transform: uppercase;
    z-index: 2;
}
div.news > a.people {
    background-color: #9600B4;
}
div.news > a.boxing {
    background-color: #EB1E00;
}
div.news > a.business {
    background-color: #00A53C;
}
div.news > a.people:before {
    content: "people";
}
div.news > a.boxing:before {
    content: "boxing";
}
div.news > a.business:before {
    content: "business";
}