vertical-align各属性对比

测试用代码

<!DOCTYPE html>
<html>
<head>

    <style>
        #dd {
            //line-height: 300px;
            background-color: gray;
            position: relative;
            font-size: 60px;
            //height: 300px;
        }
        #dd > .middle {
            position: absolute;
            top: 50%;
            height: 1px;
            background-color: black;
            left: 0;
            right: 0px;
        }
        #dd span {
            background-color: green;

        }
    </style>
  </head>
<body>
    <div id="dd">
        <img style="height:60px;width:100px;background-color:red;"><span>xg</span>
        <div class="middle"></div>
    </div>
</body>
</html>