How to add a multiple divs to an existing parent div through code-behind

Question

I'm having trouble adding multiple new divs I create in the code-behind of my aspx file. I am getting the error "Cannot get inner content of because the contents are not literal"

I have tried adding the created item as a div, asp:Panel, asp:Literal, changing the parent item from div to asp:Panel.

protected void Page_Load(object sender, EventArgs e)
{
   var newDiv = new System.Web.UI.HtmlControls.HtmlGenericControl();
   newDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.BorderStyle,"Solid");
   newDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.BorderColor,"Gray");
   newDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.BorderWidth, "5px");
   newDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.Width, "300px");
   newDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.Height,"200px");
   newDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.BackgroundColor, "White");
   newDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.Cursor, "Pointer");
   newDiv.Style.Add(System.Web.UI.HtmlTextWriterStyle.Display, "Inline-Block");
   newDiv.Attributes.Add("runat", "server");

   int i = 0;
   while(i < 10)
   {
       parentDiv.Controls.Add(newDiv);
       i++;
   }
}

I keep getting "Cannot get inner content of because the contents are not literal"

Any help would be appreciated!