Highlight Selected Checkbox items

Hi..
we are binding checkboxlist values dynamically and comparing with some condition and if matches than that Checkboxlist item should be selected and highlighted and is working but when we do button click or dropdownlist selected index changed, only highlighted color disappears ..do i need to write any updation for the below code
 chkEnv.Items[i].Selected = true;
chkEnv.Items[i].Attributes.Add("style", "background-color: yellow;");