css/CSS2/positioning/absolute-non-replaced-height-003.xht

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<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>CSS Test: Absolutely positioned, non-replaced elements, vertical centering</title>
        <link rel="author" title="Microsoft" href="http://www.microsoft.com/" />
        <link rel="reviewer" title="Gérard Talbot" href="http://www.gtalbot.org/BrowserBugsSection/css21testsuite/" /> <!-- 2012-08-31 -->
        <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-height" />
		<link rel="match" href="absolute-non-replaced-height-003-ref.xht" />

        <meta name="assert" content="An absolutely positioned non-replaced element's padding box (which is the area painted by background-color of the element) will be vertically centered within its containing block only if both 'margin-top' and 'margin-bottom' have equal values and if 'top' and 'bottom' have equal values. An absolutely positioned non-replaced element's margin box will be vertically centered within its containing block only if 'top' and 'bottom' have equal values." />
        <style type="text/css">
            #div1
            {
                border: solid black;
                height: 3in;
                position: relative;
                width: 3in;
            }
            div div
            {
                background: blue;
                bottom: 0.5in;
                height: 1in;
                margin-bottom: auto;
                margin-top: auto;
                position: absolute;
                top: 0.5in;
                width: 100%;
            }

		/*

		0.5in : top
	+
		auto (solve): margin-top
	+
		0 : border-top-width
	+
		0 : padding-top
	+
		1in : height
	+
		0 : padding-bottom
	+
		0 : border-bottom-width
	+
		auto (solve) : margin-bottom
	+
		0.5in : bottom
	=============
		3.0in : height of containing block

	So, margin-bottom and margin-top must use 0.5in so that the equation gets balanced.

		*/


        </style>
    </head>
    <body>
        <p>Test passes if a blue rectangle is <strong>vertically centered</strong> in an hollow black square.</p>
        <div id="div1">
            <div></div>
        </div>
    </body>
</html>