Untitled

<div id="catmainsvg">
<img id="preview" onclick="switchvisibility('catmaininfo'); getElementById('catmainsvg').style.width='100%'; switchSVG(); return true" title="Click to switch to SVG mode ! Pan Center Zoom tool will be available !" src="catalog/jpcl2/M1748822.jpg" alt="Current item image">
<embed style="display:none;" type="image/svg+xml" src="catalog/jpcl2/M1748822.svg" width="100%" height="100%" id="svgmap" name="svgmap" wmode="transparent" pluginspage="http://www.adobe.com/svg/viewer/install/">
</div>

and 
in my style.css file
div#catmainsvg{z-index:1; text-align:center; float:left;}


sometimes the svg comes nicely aligned top left sometimes simply goes bellow few tens of pixels and is no more aligned to top as I woul like to see it !

Any ideea ?