Add a css function as
.focusfld
{
background-color: #FFFFCC;
}
then add its reference in aspx page like:
<link href="Style/StyleSheet.css" rel="stylesheet" type="text/css" />
Write a Javacript funtion in aspx as:
function Fun1(ctrl)
{
ctrl.className = 'focusfld';
}
and in the pageLoad() add:
TextBox1.Attributes.Add("onFocus", "Fun1(this)");