Image:

Your browser's rendering:

$\colorbox[rgb]{0.8,1,1}{$HH$}$

Source Code:

    <math> 
      <mstyle background='#ccffff'> 
        <mi>H</mi> 
        <mspace width='-10px'/> 
        <mi>H</mi> 
      </mstyle> 
    </math>