How do I make Standards mode work as well as quirks mode?

<!-- Deliberately no DocType to induce Quirks Mode -->
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <style type="text/css">
        Input.quirks
        {
            margin: 1px 0px 1px 0px;
            border: solid black 1px;
        }
    </style>
</head>
<body>
Should work in Quirks Mode <br />
    <input class="quirks" type="text" style="width: 300px;" /><br />
    <input class="quirks" type="text" style="width: 147px;" /><img src="./Graphics/SpacerPixel.gif" border="0" /><input class="quirks" type="text" maxlength="25" style="width: 150px;" /><br />
    <input class="quirks" type="text" style="width: 94px;" /><img src="./Graphics/SpacerPixel.gif" border="0" /><input class="quirks" type="text" style="width: 100px;" /><img src="./Graphics/SpacerPixel.gif" border="0" /><input class="quirks" type="text" value="DA8 1DE" style="width: 100px;" />
</body>
</html>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
     "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

300px + 5px = 305px
145px + 150px + 2*5px = 305px
90px + 100px + 100px + 3*5px = 305px