picture size in em - update 2

Hi, thanks a lot for these great module. The modul works fine and i place the block in the header region. But i like to define the Header image in "em" to scale it in the browser like types. I try this...

  <div id="header_img"><?php print $header ?></div>  

in page.tlp.php and in the css..

#header_img, img { 
   height: 3.13em;
   width: 18.75em;
   display: block;
}

This is the only way i find, because now all images (e.g. logo) have this scale.

Sorry for my level in english. I hope you understand and maybe you have an answer.

best regards

buntstich