To display HTML (such as Top Navigation Dropdown) over a Silverlight application (such as Power Pivot) you’ll need to contact the the Silverlight application's developer and have them set the control’s "windowless" parameter to "true" to ensure it does not overlay other page elements.

This can be accomplished by the application developer using the param tag as shown in the bold line below:

Example Code

<object data="data:application/x-silverlight-2," type="application/x-silverlight-2" width="100%" height="100%">
<param name="source" value="ClientBin/HTMLAndSilverlight.xap"/>
<param name="onError" value="onSilverlightError" />
<param name="background" value="white" />
<param name="minRuntimeVersion" value="4.0.50401.0" />
<param name="autoUpgrade" value="true" />
<param name="windowless" value="true" />
<a href="" style="text-decoration:none">
<img src="" alt="Get Microsoft Silverlight" style="border-style:none"/>