css/CSS2/positioning/absolute-non-replaced-height-010.xht

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>CSS Test: Absolutely positioned, non-replaced elements, 'margin-top' and 'margin-bottom' set to '0'</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="The 'auto' values for 'margin-top' and 'margin-bottom' are set to '0', when 'top' is 'auto' and 'height' and 'bottom' are not 'auto'." />
        <style type="text/css">
            #div1
            {
                border: solid black;
                height: 3in;
                position: relative;
                width: 3in;
            }
            div div
            {
                background: blue;
                bottom: 1in;
                height: 1in;
                margin-bottom: auto;
                margin-top: auto;
                position: absolute;
                top: auto;
                width: 100%;
            }

            /*

		 auto (to solve) : top
	+
		 auto (to solve): margin-top
	+
		 0 : border-top-width
	+
		 0 : padding-top
	+
		 1in : height
	+
		 0 : padding-bottom
	+
		 0 : border-bottom-width
	+
		 auto (to solve): margin-bottom
	+
		1in : bottom
	=============
		3in  : height of containing block


	"
	'top' is 'auto', 'height' and 'bottom' are not 'auto',
	then set 'auto' values for 'margin-top' and 'margin-bottom' to 0,
	and solve for 'top'
	"

	so this brings:

		 auto (to solve) : top
	+
		 0 (set): margin-top
	+
		 0 : border-top-width
	+
		 0 : padding-top
	+
		 1in : height
	+
		 0 : padding-bottom
	+
		 0 : border-bottom-width
	+
		 0 (set): margin-bottom
	+
		1in : bottom
	=============
		3in  : height of containing block

		So, top must use 1in in order to balance the equation


            */

        </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>