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    Stacking context example 2

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    Stacking context example 2

    This is a very simple example, but it is the key for understanding the concept of stacking context. There are the same four DIVs of the previous example, but now z-index properties are assigned on both levels of the hierarchy.

    Stacking context example 2

    You can see that DIV #2 (z-index: 2) is above DIV #3 (z-index: 1), because they both belong to the same stacking context (the root one), so z-index values rule how elements are stacked.

    What can be considered strange is that DIV #2 (z-index: 2) is above DIV #4 (z-index: 10), despite their z-index values. The reason is that they do not belong to the same stacking context. DIV #4 belongs to the stacking context created by DIV #3, and as explained previously DIV #3 (and all its content) is under DIV #2.

    To better understand the situation, this is the stacking context hierarchy:

    • root stacking context
      • DIV #2 (z-index 2)
      • DIV #3 (z-index 1)
        • DIV #4 (z-index 10)
    Note: It is worth remembering that in general the HTML hierarchy is different from the stacking context hierarchy. In the stacking context hierarchy, elements that do not create a stacking context are collapsed on their parent.

    Example source code

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html>
    <head><style type="text/css">
    
    div { font: 12px Arial; }
    
    span.bold { font-weight: bold; }
    
    #div2 { z-index: 2; }
    #div3 { z-index: 1; }
    #div4 { z-index: 10; }
    
    #div1,#div3 {
       height: 80px;
       position: relative;
       border: 1px dashed #669966;
       background-color: #ccffcc;
       padding-left: 5px;
    }
    
    #div2 {
       opacity: 0.8;
       position: absolute;
       width: 150px;
       height: 200px;
       top: 20px;
       left: 170px;
       border: 1px dashed #990000;
       background-color: #ffdddd;
       text-align: center;
    }
    
    #div4 {
       opacity: 0.8;
       position: absolute;
       width: 200px;
       height: 70px;
       top: 65px;
       left: 50px;
       border: 1px dashed #000099;
       background-color: #ddddff;
       text-align: left;
       padding-left: 10px;
    }
    
    
    </style></head>
    
    <body>
    
    <br />
    
    <div id="div1">
    <br /><span class="bold">DIV #1</span>
    <br />position: relative;
       <div id="div2">
       <br /><span class="bold">DIV #2</span>
       <br />position: absolute;
       <br />z-index: 2;
       </div>
    </div>
    
    <br />
    
    <div id="div3">
    <br /><span class="bold">DIV #3</span>
    <br />position: relative;
    <br />z-index: 1;
       <div id="div4">
       <br /><span class="bold">DIV #4</span>
       <br />position: absolute;
       <br />z-index: 10;
       </div>
    </div>
    
    </body></html>
    

    See also

    Original Document Information

     

    Document Tags and Contributors

    Last updated by: Jeremie,