recently i have been trying to create modalpopupextender and it worked just fine. then i found something that confuse me, which is the style in asp panel are set to display none
<asp:Panel ID="pnlPopup" runat="server" CssClass="modalPopup" Style="display: none">
but, when i'm running it in browser, it changed to
<div id="pnlPopup" class="modalPopup" style="position: fixed; z-index: 10002; left: 810px; top: 186px;">
fyi, I follow the tutorial from this link
https://www.aspsnippets.com/Articles/Open-Show-ASPNet-AJAX-ModalPopupExtender-Modal-Popup-on-Page-Load-in-ASPNet.aspx
so, the question is, where is that style coming from? and when I try to put any style to replace Style="display: none", but it keep show style="position: fixed; z-index: 10002; left: 810px; top: 186px;".