当容器div中的绝对位置时，图像链接不可单击

Question

我有一个带有背景图像的div容器和背景图像上的两个图标。问题是当我将鼠标指向图标时，它不允许点击图像并打开超链接。这是我得到的代码：

＆＃13;

＆＃13;

<style type="text/css">
    .containerdiv { float: left; position: relative; left: -10px; top: -10px;}
    .cornerimage1 { position: absolute; top: 75%; left: 0.5%;}
    .cornerimage2 { position: absolute; bottom: 23%; left: 0.5%;}
</style>

<div class="containerdiv">
    <iframe src="images/mybackground.jpg" width="550" height="314" frameborder="0" scrolling="no"></iframe>
    <a href="//facebook.com" target="_blank" rel="alternate"><img class="cornerimage1" src="images/iconfacebook.png" alt="" width="90" height="34"></a>
    <a href="//twitter.com" target="_blank" rel="alternate"><img class="cornerimage2" src="images/icontwitter.png" alt="" width="90" height="34"></a>
</div>

＆＃13;

＆＃13;

＆＃13;