Can you blur the content beneath/behind a div? [duplicate]

Answer 1

If you want to enable unblur, you cannot just add the blur CSS to the body, you need to blur each visible child one level directly under the body and then remove the CSS to unblur. The reason is because of the "Cascade" in CSS, you cannot undo the cascading of the CSS blur effect for a child of the body. Also, to blur the body's background image you need to use the pseudo element :before

//HTML


    

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Gumbo beet greens corn soko endive gumbo gourd. Parsley shallot courgette tatsoi pea sprouts fava bean collard greens dandelion okra wakame tomato. Dandelion cucumber earthnut pea peanut soko zucchini.
                    
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Gumbo beet greens corn soko endive gumbo gourd. Parsley shallot courgette tatsoi pea sprouts fava bean collard greens dandelion okra wakame tomato. Dandelion cucumber earthnut pea peanut soko zucchini.
                    
Turnip greens yarrow ricebean rutabaga endive cauliflower sea lettuce kohlrabi amaranth water spinach avocado daikon napa cabbage asparagus winter purslane kale. Celery potato scallion desert raisin horseradish spinach carrot soko. Lotus root water spinach fennel kombu maize bamboo shoot green bean swiss chard seakale pumpkin onion chickpea gram corn pea. Brussels sprout coriander water chestnut gourd swiss chard wakame kohlrabi beetroot carrot watercress. Corn amaranth salsify bunya nuts nori azuki bean chickweed potato bell pepper artichoke.
                    
Gumbo beet greens corn soko endive gumbo gourd. Parsley shallot courgette tatsoi pea sprouts fava bean collard greens dandelion okra wakame tomato. Dandelion cucumber earthnut pea peanut soko zucchini.
                    
Turnip greens yarrow ricebean rutabaga endive cauliflower sea lettuce kohlrabi amaranth water spinach avocado daikon napa cabbage asparagus winter purslane kale. Celery potato scallion desert raisin horseradish spinach carrot soko. Lotus root water spinach fennel kombu maize bamboo shoot green bean swiss chard seakale pumpkin onion chickpea gram corn pea. Brussels sprout coriander water chestnut gourd swiss chard wakame kohlrabi beetroot carrot watercress. Corn amaranth salsify bunya nuts nori azuki bean chickweed potato bell pepper artichoke.
                
            
        
    


//CSS

/* Blur - doesn't work on IE */

.blur-on, .blur-element {
    -webkit-filter: blur(10px);
    -moz-filter: blur(10px);
    -o-filter: blur(10px);
    -ms-filter: blur(10px);
    filter: blur(10px);

    -webkit-transition: all 5s linear;
    transition        : all 5s linear;
    -moz-transition   : all 5s linear;
    -webkit-transition: all 5s linear;
    -o-transition     : all 5s linear;
}
.blur-off {
    -webkit-filter: blur(0px) !important;
    -moz-filter   : blur(0px) !important;
    -o-filter     : blur(0px) !important;
    -ms-filter    : blur(0px) !important;
    filter        : blur(0px) !important;
}
.blur-bgimage:before {
    content: "";
    position: absolute;
    height: 20%; width: 20%;
    background-size: cover;
    background: inherit;
    z-index: -1;

    transform: scale(5);
    transform-origin: top left;
    filter: blur(2px);       
    -moz-transform: scale(5);
    -moz-transform-origin: top left;
    -moz-filter: blur(2px);       
    -webkit-transform: scale(5);
    -webkit-transform-origin: top left;
    -webkit-filter: blur(2px);
    -o-transform: scale(5);
    -o-transform-origin: top left;
    -o-filter: blur(2px);       

    transition        : all 5s linear;
    -moz-transition   : all 5s linear;
    -webkit-transition: all 5s linear;
    -o-transition     : all 5s linear;
}


//Javascript

function blurBehindPopup() {
    if(blurredElements.length == 0) {
        for(var i=0; i < document.body.children.length; i++) {
            var element = document.body.children[i];
            if(element.id && element.id != 'fullscreen-popup' && element.isVisible == true) {
                classie.addClass( element, 'blur-element' );
                blurredElements.push(element);
            }
        }
    } else {
        for(var i=0; i < blurredElements.length; i++) {
            classie.addClass( blurredElements[i], 'blur-element' );
        }
    }
}
function unblurBehindPopup() {
    for(var i=0; i < blurredElements.length; i++) {
        classie.removeClass( blurredElements[i], 'blur-element' );
    }
}

Full Working Example Link