get div id on codebehind page

Question

HI,

  .aspx page - 

<h3 id="h3_up">Upload</h3>

<div id="div_up">

<ul style="padding:0px">

<li id="HRData" runat="server">

 

I want to get these id on code behind for enable and disable data.LIke

 

h3_up.Visible = false;

div_up.Visible = true;

HRData.Visible = True;

 

Please help.