I use this Is it possible to use -webkit-filter: blur(); on background-image? solution to make blurry backgroung image and it works great! But I want to make some <         
        
use -webkit-filter: blur(2px) in .background div not in .content div.
Here is your updated code:
.content{
width: 70%;
height: 70%;
border:2px solid;
border-radius:20px;
position: fixed;
top: 15%;
left: 15%;
z-index:10;
background-color: rgba(168, 235, 255, 0.2);
filter: blur(2px); 
-moz-filter: blur(2px);
-o-filter: blur(2px); 
-ms-filter: blur(2px);
}
.background{
width:100%;
height:100%;
background-image:url('http://www.travel.com.hk/region/time_95.jpg');
z-index:0;
position:absolute;
 -webkit-filter: blur(2px);
}
If it has to be dynamic, you should have some trouble, but you can have somewhere to start with this :
HTML
<div class="background"></div>
<div class="mask">
    <div class="bluredBackground"></div>
</div>
<div class="content"></div>
CSS
.content {
    width: 70%;
    height: 70%;
    border:2px solid;
    border-radius:20px;
    position: fixed;
    top: 15%;
    left: 15%;
    z-index:10;
    background-color: rgba(168, 235, 255, 0.2);
}
.background {
    width:100%;
    height:100%;
    background-image:url('http://www.travel.com.hk/region/time_95.jpg');
    z-index:2;
    position:fixed;
}
.bluredBackground {
    width:100%;
    height:100%;
    display:block;
    background-image:url('http://www.travel.com.hk/region/time_95.jpg');
    z-index:1;
    position:absolute;
    top:-20%;
    left:-20%;
    padding-left:20%;
    padding-top:20%;
    -webkit-filter: blur(2px);
}
.mask {
    width: 70%;
    height: 70%;
    border:2px solid;
    border-radius:20px;
    position: fixed;
    top: 15%;
    left: 15%;
    z-index:10;
    overflow:hidden;
}
FIDDLE