Cfinput tooltip css styling

Hi!

I have the code below and I want to know how to create a css rule to add style to the tooltip within cfinput. It is displayed by default, however, i want to format how it looks. Any ideas?

<div class="container">

<h1> Create user </h1>

<cfform  id="form" action="processusercreation.cfm" method="post" >

<table>

<tr>
<td id="formleft">
  Username
</td>
<td id="formright">
     <cfinput type="text"
        tooltip="Desired username, with 20 letters and numbers, no spaces"
        required="yes"
        validate="regular_expression"
        pattern="^[a-zA-Z0-9]+$"
        message="~Hey, there is something wrong with your username~"
        validateat="onsubmit,onserver"
        name="Username"
  maxlength="17">
     </td>
</tr>