Add css class dynamically from code-behind file for HTML/ASP.NET controls

The tip shows how to assign CSS class dynamically through ASP.NET code behind file for HTML controls and ASP.NET controls.

Sample CSS:

.clsbgcolor
{
  background-color:red;
}

We can't access HTML controls directly in code behind file. So in order to access HTML control add runat="server" tag to HTML code.

<div id="mydiv" runat="server"></div>

In code behind assign CSS class to div control

protected void Page_Load(object sender, EventArgs e)
{
     mydiv.Attributes.Add("class", "clsbgcolor");
}

For ASP.NET server side controls directly we can use cssClass property.

<asp:panel runat="server" id="pnl"></asp:panel>

protected void Page_Load(object sender, EventArgs e)
{
    pnl.CssClass = "clsbgcolor"
}

Note: If you are using external CSS file make sure that you have added reference to page.