Keeping image from moving around header

Hello,

I recently placed a banner ad on my template in the header. The ad is positioned correctly however, Whenever you resize the window the image overlaps the banner horizontally but does not move vertically. I want the image to stay locked in place. How would I go about doing this? Below is the css and the corresponding HTML code.

#header_icons {     

float:right;
/*   padding-top:0px;*/
    width:1000px;
margin: 0 auto;
position: relative;

padding-bottom:10px;

} 

#header_icons img { 

float:right;
    height:110px;
    width:365px;
    margin: 45px 158px 25px 10px;
    margin-left:10px;
position: absolute;
right: -1px;
top: 20px;
z-index: 3;

}

<div id="header_icons" class="center">
<a href="https://www.pbpexecutivereports.com/mn.asp?O=ZB1">
<img src="https://www.managersareheroes.com/wp-content/uploads/2013/04/mahbuttonlo.gif"/>
</a></div>

Thank you.