It is possible with CSS3 :

#myDiv {    -webkit-filter: blur(20px);    -moz-filter: blur(20px);    -o-filter: blur(20px);    -ms-filter: blur(20px);    filter: blur(20px);    opacity: 0.4;}

Example here => jsfiddle

You made me want to try, so I did, check out the example here:

http://codepen.io/Edo_B/pen/cLbrt

Using:

1. HW Accelerated CSS filters
2. JS for class assigning and arrow key events
3. Images CSS Clip property

that's it.

I also believe this could be done dynamically for any screen if using canvas to copy the current dom and blurring it.

[Edit] In the future (mobile) Safari 9 there will be -webkit-backdrop-filter for exactly this. See this pen I made to showcase it.

I thought about this for the last 4 weeks and came up with this solution.

Live Demo

[Edit]I wrote a more indepth post on CSS-Tricks

This technique is using CSS Regions so the browser support is not the best at this moment. (http://caniuse.com/#feat=css-regions)

The key part of this technique is to split apart content from layout by using CSS Region. First define a .content element with flow-into:content and then use the appropriate structure to blur the header.

The layout structure:

<div class="phone"> <div class="phone__display">  <div class="header">    <div class="header__text">Header</div>    <div class="header__background"></div>  </div>  <div class="phone__content">  </div> </div></div>

The two important parts of this layout are .header__background and .phone__content - these are the containers where the content should flow though.

Using CSS Regions it is simple as flow-from:content (.content is flowing into the named region content)

Now comes the tricky part. We want to always flow the content through the .header__background because that is the section where the content will be blured. (using webkit-filter:blur(10px);)

This is done by transfrom:translateY(-$HeightOfTheHeader) the .content to ensure that the content will always flow though the .header__background. This transform while always hide some content beneath the header. Fixing this is ease adding

.header__background:before{  display:inline-block;  content:'';  height:$HeightOfTheHEader}

to accommodate for the transform.

This is currently working in:

• Chrome 29+ (enable 'experimental-webkit-features'/'enable-experimental-web-platform-features')
• Safari 6.1 Seed 6
• iOS7 (slow and no scrolling)