simple responsive CSS/HTML - centering an image on mobile

Hello,

For some reason, my ask-a-nurse image on mobile is not centered. It's the nurse image at the top of the page.

The buttons under it are centered on mobile, but the nurse picture isn't. Could you tell me how to center it and keep everything else the same on all devices?

www.idiaper.com

<div id="iconDiv-nurse" style="text-align:center">
<a id="nurseImg" href="http://www.idiaper.com/Ask-A-Nurse_ep_29.html"><img id="left-nurse1" alt="ask a nurse button" src="http://www.idiaper.com/assets/images/left-nurse2.jpg"></a><div id="nurseLinks">
  <a href="http://www.idiaper.com/womens-diapers"><img alt="for women button" src="http://www.idiaper.com/assets/images/women-nurse2.jpg"></a><a 
  href="http://www.idiaper.com/Auto-Reorder_ep_43-1.html"><img alt="auto-reorder button button" src="http://www.idiaper.com/assets/images/auto-ship-nurse3.jpg"></a><a 
  href="http://www.idiaper.com/mens-diapers"><img alt="for men button" src="http://www.idiaper.com/assets/images/men-nurse.jpg"></a><a 
  href="http://www.idiaper.com/overnight-adult-diapers"><img alt="overnight products button" src="http://www.idiaper.com/assets/images/overnight-nurse2.jpg"></a><a 
  href="http://www.idiaper.com/adult-pullups"><img alt="pull ups button" src="http://www.idiaper.com/assets/images/pull-ups-nurse2.jpg"></a><a 
  href="http://www.idiaper.com/adult-cloth-diapers-briefs"><img alt="adult cloth diapers button" src="http://www.idiaper.com/assets/images/acd-nurse2.jpg"></a>

</div> 
</div>

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#nurse-cat
{
float:left;
background-color:#3690cf;
color:#fff;
font-weight:normal;
padding:1%;
padding-right:2%;
}

#nurse-cat a,#nurse-cat a:hover, #nurse-cat a:visited
{
text-decoration:underline;
}

#nurse-cat a:hover
{
color:#9fa2a3;
}
#nurse-cat a:visited
{
color:#46c4ff;
}

#nurse-cat img
{
float:left;
margin-right:10px;
}


@media screen and (max-width: 600px){

#nurse-cat img
{
width:135px;
}

}

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