Background blur with CSS

You can use a pseudo-element to position as the background of the content with the same image as the background, but blurred with the new CSS3 filter.

You can see it in action here: http://codepen.io/jiserra/pen/JzKpx

I made that for customizing a select, but I added the blur background effect.

OCT. 2016 UPDATE

Since the -moz-element() property doesn't seem to be widely supported by other browsers except to FF, there's an even easier technique to apply blurring without affecting the contents of the container. The use of pseudoelements is ideal in this case in combination with svg blur filter.

Check the demo using pseudo-element

(Demo was tested in FF v49, Chrome v53, Opera 40 - IE doesn't seem to support blur either with css or svg filter)

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The only way (so far) of having a blur effect in the background without js plugins, is the use of -moz-element() property in combination with the svg blur filter. With -moz-element() you can define an element as a background image of another element. Then you apply the svg blur filter. OPTIONAL: You can utilize some jQuery for scrolling if your background is in fixed position.

See my demo here

I understand it is a quite complicated solution and limited to FF (element() applies only to Mozilla at the moment with -moz-element() property) but at least there's been some effort in the past to implement in webkit browsers and hopefully it will be implemented in the future.

In recent versions of major browsers you can use backdrop-filter property.

HTML

<div>backdrop blur</div>

CSS

div {
    -webkit-backdrop-filter: blur(10px);
    backdrop-filter: blur(10px);
}

or if you need different background color for browsers without support:

div {
    background-color: rgba(255, 255, 255, 0.9);
}

@supports (-webkit-backdrop-filter: none) or (backdrop-filter: none) {
    div {
        -webkit-backdrop-filter: blur(10px);
        backdrop-filter: blur(10px);
        background-color: rgba(255, 255, 255, 0.5);  
    }
}

Demo: JSFiddle

Docs: Mozilla Developer: backdrop-filter

Is it for me?: CanIUse