First-child doesnt work

Hi.

I am designing a new WordPress theme and everything goes fine until I post enough posts to “activate” pagination. Then all of a sudden the CSS-selector :first-child stops working.

I am trying to give the newest post different styling and :first-child is perfect, but it won’t work like I thought. Is there an easy fix to my problem or should I look for a new way to style the newest post seperately? If so, any suggestions?

I am using the twentyeleven-theme. Any help is appreciated. 🙂

Thanks!