纯CSS3实现聊天框小尖角、气泡效果、空心效果

下面是实现用css3制作的聊天气泡的效果，原理和效果都在代码里面，大家有兴趣的拿去测试吧！免去了使用图片的繁琐和不便修改的问题，效果如下图所示：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
    <style type="text/css">
        .tag
        {
            width: 300px;
            height: 100px;
            border: 5px solid #09F;
            position: relative;
        }
        .tag em
        {
            display: block;
            border-width: 20px;
            position: absolute;
            bottom: -40px;
            left: 100px;
            border-style: solid dashed dashed;
            border-color: #09F transparent transparent;
            font-size: 0;
            line-height: 0;
        }
        .tag span
        {
            display: block;
            border-width: 20px;
            position: absolute;
            bottom: -33px;
            left: 100px;
            border-style: solid dashed dashed;
            border-color: #FFF transparent transparent;
            font-size: 0;
            line-height: 0;
        }
    </style>
</head>
<body>
    <div class="tag">
        <em></em>CSS气泡框实现
    </div>
    <div class="tag" style="margin-top: 100px">
        <em></em><span></span>CSS气泡框实现
    </div>
</body>
</html>