苹果的叠加层似乎不仅仅是透明度.关于如何用CSS和可能的JS实现这种效果的任何想法?

我正在尝试使用HTML5,CSS3和JavaScript创建一个可以在webkit浏览器上运行的iOS 7风格磨砂外观.
从技术上讲,给出以下HTML:
<style>
#partial-overlay {
width: 100%;
height: 20px;
background: rgba(255, 255, 255, .2); /* TODO frost */
position: fixed;
top: 0;
left: 0;
}
</style>
<div id="main-view">
<div style="width: 50px; height: 50px; background: #f00"></div>
To my left is a red box<br>
Now there is just text<br>
Text that goes on for a few pixels <br>
or even more
</div>
<div id="partial-overlay">
Here is some content
</div>
Run Code Online (Sandbox Code Playgroud)
我想-webkit-filter: blur(5px)在水平的前20px处应用类似a的东西#main-view.
如果CSS被修改为#partial-overlay { width: 20px; height: …