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    Adding z-index

    « CSS « Understanding CSS z-index

    Adding z-index

    The first example, Stacking without z-index, explains how stacking is arranged by default. If you want to specify a different stacking order, you have to position an element and use the z-index property.

    This property is assigned with an integer value (positive or negative), which represents the position of the element along the z-axis. If you are not familiar with the z-axis, imagine the page has several layers one above the other. Each layer is numbered. A layer with a greater number is rendered above layers with smaller numbers.

    Warning: z-index only has an effect if an element is positioned.

    • bottom: furthest from the observer
    • ...
    • Layer -3
    • Layer -2
    • Layer -1
    • Layer 0 default rendering layer
    • Layer 1
    • Layer 2
    • Layer 3
    • ...
    • top: closest to the observer

    Notes:

    • When no z-index property is specified, elements are rendered on the default rendering layer 0 (zero).
    • If several elements share the same z-index value (i.e. they are placed on the same layer), stacking rules explained in the section Stacking without z-index apply.

    In the next example, the layers' stacking order is rearranged using z-index. The z-index of DIV#5 has no effect since it is not a positioned element.

    Example of stacking rules modified using z-index

    Example source code

    <!DOCTYPE html>
    <html>
    <head>
        <meta charset="UTF-8">
        <title>Adding z-index</title>
        <style type="text/css">
    
        div {
            opacity: 0.7;
            font: 12px Arial;
        }
    
        span.bold { font-weight: bold; }
    
        #normdiv {
            z-index: 8;
            height: 70px;
            border: 1px dashed #999966;
            background-color: #ffffcc;
            margin: 0px 50px 0px 50px;
            text-align: center;
        }
    
        #reldiv1 {
            z-index: 3;
            height: 100px;
            position: relative;
            top: 30px;
            border: 1px dashed #669966;
            background-color: #ccffcc;
            margin: 0px 50px 0px 50px;
            text-align: center;
        }
    
        #reldiv2 {
            z-index: 2;
            height: 100px;
            position: relative;
            top: 15px;
            left: 20px;
            border: 1px dashed #669966;
            background-color: #ccffcc;
            margin: 0px 50px 0px 50px;
            text-align: center;
        }
    
        #absdiv1 {
            z-index: 5;
            position: absolute;
            width: 150px;
            height: 350px;
            top: 10px;
            left: 10px;
            border: 1px dashed #990000;
            background-color: #ffdddd;
            text-align: center;
        }
    
        #absdiv2 {
            z-index: 1;
            position: absolute;
            width: 150px;
            height: 350px;
            top: 10px;
            right: 10px;
            border: 1px dashed #990000;
            background-color: #ffdddd;
            text-align: center;
        }
    
        </style>
    </head>
    
    <body>
    
        <br /><br />
    
        <div id="absdiv1">
            <br /><span class="bold">DIV #1</span>
            <br />position: absolute;
            <br />z-index: 5;
        </div>
    
        <div id="reldiv1">
            <br /><span class="bold">DIV #2</span>
            <br />position: relative;
            <br />z-index: 3;
        </div>
    
        <div id="reldiv2">
            <br /><span class="bold">DIV #3</span>
            <br />position: relative;
            <br />z-index: 2;
        </div>
    
        <div id="absdiv2">
            <br /><span class="bold">DIV #4</span>
            <br />position: absolute;
            <br />z-index: 1;
        </div>
    
        <div id="normdiv">
            <br /><span class="bold">DIV #5</span>
            <br />no positioning
            <br />z-index: 8;
        </div>
    
    </body>
    </html>
    

    See also

    Original Document Information

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    Last updated by: xfq,