CSS - Change specific box-shadow in box-shadows list

Question

How can we override one specific value and preserve all other values in box-shadow list like this:

div{

    box-shadow: 0 0 0 5px #00ff00 ,  0 0 0 10px #ff0000 ,  0 0 0 15px #0000ff ; 

}

Let's say we want to override only the second value without losing others:

div.with-another-shadow{

    box-shadow:       ???         ,  0 0 0 5px #abcdef ,       ???           ;  

}

Seems like it is possible only when we are copy-pasting the first and the third values too. It is not working not with auto and not with inherit .

Is it possible to achieve this only with css or we need to use jQuery or JavaScript' getComputedStyle method or something ?

Here is the playground: http://jsfiddle.net/cherniv/uspTj/5/

PS Seems like it is relevant to multiple background images list too..

Answer 1

This is not a real solution to the general case, but a trick to solve the particular case of your fiddle:

div{
    box-shadow: 0 0 0 5px green,  0 0 0 10px #ff0000 ,  0 0 0 15px blue;    
    position: relative;
}

div:nth-of-type(2):after {
    content: '';
    position: absolute;
    left: 0px;
    right: 0px;
    top: 0px;
    bottom: 0px;
    margin: -5px;
    box-shadow: 0 0 0 5px yellow;    
}

demo

I am creating a pseudo element to hold the second shadow, and set a margin (negative) to get it past the first shadow, so that I won't draw on it.

Here is another demo, changing the value thru JavaScript

demo2

The script is the following

function change () {
    var elem = document.getElementById("test");
    var style = window.getComputedStyle(elem);
    var boxShadow = style.boxShadow;
    var arrayBoxShadows = parseFirstComma (boxShadow);

    var newData = elem.dataset.boxshadow;
    var arrayNewData = parseFirstComma (newData);
    boxShadow = "";
    var nmax = Math.min (arrayBoxShadows.length, arrayNewData.length)
    for (var n = 0, lenR = nmax; n < lenR; n++) {
        if (n > 0) {
            boxShadow = boxShadow + ", ";
        }
        if (arrayNewData[n] == "inherit") {
            boxShadow = boxShadow + arrayBoxShadows[n];
        } else {
            boxShadow = boxShadow + arrayNewData[n];

        }
    }
    if (arrayNewData.length > nmax) {
        for (var n = nmax, lenR = arrayNewData.length; n < lenR; n++) {
            if (n > 0) {
                boxShadow = boxShadow + ", ";
            }
            boxShadow = boxShadow + arrayNewData[n];
        }
    }
    if (arrayBoxShadows.length > nmax) {
        for (var n = nmax, lenR = arrayBoxShadows.length; n < lenR; n++) {
            if (n > 0) {
                boxShadow = boxShadow + ", ";
            }
            boxShadow = boxShadow + arrayBoxShadows[n];
        }
    }


    elem.style.boxShadow = boxShadow;
}


function parseFirstComma (property) {
    var properties = new Array();
    var curr = "";
    var chr;
    var nested = "";

    for (inx = 0, len = property.length; inx < len; inx++) {
        chr = property[inx];
        if (chr == "(") nested += 1;
        if (chr == ")") nested -= 1;
        if (nested == 0 && chr == ",") {
            properties.push (curr);
            curr = "";
        } else {
            curr = curr + chr;
        }
    }
    if (curr.length > 0) {
        properties.push (curr);
    }
    return properties;
};

document.onkeydown = function (e) {
    e = e || window.event;
    switch(e.which || e.keyCode) {
        case 37:
            change ();
            break;
    }
}

I am retrieving the box-shadow applied to the element, and retrieve the desired override from a data value. And then, recalculate the result (using inherit as a posible value). The demo is activated pressing the left arrow.

Answer 2

Under the current CSS specification, it is not possible to override one of the values of a multiple-value attribute.

You will need to repeat the definition of the 1st and 3rd shadows in the second rule, ie

div{
    box-shadow: 0 0 0 5px #00ff00 ,  0 0 0 10px #ff0000 ,  0 0 0 15px #0000ff ; 
}

div:nth-of-type(2){
    box-shadow: 0 0 0 5px #00ff00 ,  0 0 0 10px #abcdef ,  0 0 0 15px #0000ff ; 
}

This message in the W3 mailing list suggests that it's something that's being considered http://lists.w3.org/Archives/Public/www-style/2013Apr/0711.html