HTML:
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title></title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<script type="text/javascript">
$(document).ready(function () {
$('.txt').focusin(function () {
$(this).css("background-color", "#fff4d8");
});
$('.txt').focusout(function () {
$(this).css("background-color", "#FFFFFF");
});
});
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<h1>Change Text Box Background Color On Focus</h1>
<table>
<tr>
<td>User Name:</td>
<td><asp:TextBox ID="txtName" CssClass="txt" runat="server"></asp:TextBox> </td>
</tr>
<tr>
<td>Email:</td>
<td><asp:TextBox ID="txtEmail" CssClass="txt" runat="server"></asp:TextBox></td>
</tr>
<tr>
<td>Mobile:</td>
<td><asp:TextBox ID="txtMobile" CssClass="txt" runat="server"></asp:TextBox></td>
</tr>
</table>
</div>
</form>
</body>
</html