Hide asp:panel used with a modalpopupextender on pageLoad

I have several asp:panels on a webform page which is used together with an ajax modalpopupextender.

On page load the panels are visible for a small fraction of time (depending on how fast the page loads). What's the quick and easy solution for hiding these on page load, so that they will only be visible when the modalpopupextender triggers them?

I've experienced with setting the visible="false", but that has some strange impact on the other elements on the webform.

Setting the css display:n开发者_如何学JAVAone to the panel would work, if I somehow could remove this setting when the modalpopupextender fires.

Setting the style="display: none;" to the panel solved my issue :)