Highlight current post in sidebar?

Hey there,

In my sidebar I have a list of posts from my archive. The list remains in the sidebar in the single view. I’d like to highlight the post that is currently shown in my sidebar menu.

I would prefer to do this with CSS. Now how can I assign something like a “current” class/id to the active post list tiem. The output should look something like this:

<ul>
<li>post 1</li>
<li>post 2</li>
<li id="current_post">post 3</li>
<li> post 4</li>
</ul>

When post 3 is currently shown in the single view.

Thanks in advance,

Lasse