if I read this code correctly it just counts the post in the loop and when you reacht the 3 one an if else statement occurs.
Thing is I have the same problem as the OP, but within my loop I have a statement that excludes a category this way it shows 3 posts while the loop actually is 5, so trying to target the third post and change its css can be done but it might not show for it is excluded.
Any sollutions for this?