.style.backgroundColor = "red";     } }  <form id="save"  method="post"> <input type="text" name="A"  id="C" class="textbox" onKeyUp="cc(this, 'H')"  maxlength="0"  /> <input type="text" name="A"  id="C" class="textbox" onKeyUp="cc(this, 'H')"  maxlength="0"  /> <