Put the following code in the source view. And change the font-family/font-size in the design view, with "Reuse Existing Style" button clicked or not. You will see the difference.
<head runat="server">
<title></title>
<style type="text/css">
.style1
{
font-size: x-large;
}
.classabc
{
font-family: Latha;
}
</style>
</head>
<body>
<form id="form1" runat="server">
<div class="classabc style1"></div></form>
</body>
</html>