<p>Form illustrating<code>input:focus</code></p>
<form method="post" action="http://cscie12.dce.harvard.edu/echo">
First name:
<input type="firstname"/><br/>Last name:
<input type="lastname"/><br/>Email:
<input type="email"/><br/>
<input type="submit"/>
</form>

In style element (<style type="text/css">) within head element:

input:focus { 
  background-color: #ffc; 
  border: medium solid orange;
}