How to programmatically add active style to header control links using C#?

How to programmatically add active style to header control links using C#?

I have an unordered list for my navigation in my header control. The
header control is called on each of my other pages.
<ul>
<li class="active">Home</li>
<li>About</li>
<li>Store</li>
</ul>
What is the best way to programmatically change the active class to the
About page when I load it?
I'm using C# for this project.