CustomValidator1.aspx font size:
View Sample
<html>
<head>
<title>CustomValidator Sample</title>
<link rel="stylesheet" href="/shared/netdemos.css">

<script language="C#" runat="server">
   void serverValidate ( object src, ServerValidateEventArgs arg ) {
      arg.IsValid = int.Parse ( arg.Value ) % 2 == 0;
   }

   void chkIsValid ( object src, EventArgs e ) {
      if ( Page.IsValid  ) message.InnerText = "Page has passed validation.";
   }

</script>

<script language="javascript">
<!--
   function clientValidate ( src, arg ) {
      arg.IsValid = arg.Value % 2 == 0;
      if ( !arg.IsValid ) message.innerText = "Enter an even number:";
   }
// -->
</script>

</head>

<body>
<!-- #include virtual="~/shared/top.inc -->
<div class="header"><h2>CustomValidator Sample</h2></div>

<!-- #include virtual="~/shared/viewsrc_top.inc" -->
<hr size=1 width=92%>

<center>
<form runat="server">
   <span id="message" runat="server">Enter an even number:</span>

   <p><asp:textbox id="myTextBox" size=6 runat="server" />

   <br>

   <asp:requiredfieldvalidator runat="server"
      controltovalidate="myTextBox"
      errormessage="Entry required." display="none" />

   <asp:customvalidator runat="server"
      controltovalidate="myTextBox"
      clientvalidationfunction="clientValidate"
      onServerValidate="serverValidate"
      errormessage="Not an even number. Try again." display="none" />

   <p>
   <asp:button runat="server" text="Validate" onClick="chkIsValid" />

   <asp:validationsummary runat="server"
      displaymode="singleparagraph" showsummary=false showmessagebox />

</form>
</center>

<hr size=1 width=92%>
<!-- #include virtual="~/shared/viewsrc.inc" -->

</body>
</html>