definition for 'visible' and no extension method

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C#

ASP.NET

i have a div that add runat="server" to it

<div id="divinsert"   runat="server" Visible="False" ">

at first ==>div Visible is "False"
after press a button it will be show
divinsert.visible = true;

then on div
i has a button to close div with this code
divinsert.visible = false;

how can i add attach my proj
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this error was appear:

System.Web.UI.HtmlControls.HtmlGenericControl' does not contain a definition for 'visible' and no extension method 'visible' accepting a first argument of type 'System.Web.UI.HtmlControls.HtmlGenericControl' could be found (are you missing a using directive or an assembly reference?)