How to change CSS class of a HTML page element using ASP.NET?

I have several <li> elements with different id's on ASP.NET page:

<li id="li1" class="class1">
<li id="li2" class="class1">
<li id="li3" class="class1">

and can change their class using JavaScript like this:

li1.className="class2"

But is there a way to change <li> element class using ASP.NET? It could be something like:

WebControl control = (WebControl)FindControl("li1");
control.CssClass="class2";

But FindControl() doesn't work as I expected. Any suggestions?

Thanks in advance!