How do I choose the last 2 items in a list with css nth-child?

Unfortunately it's impossible.. Disregard this answer and look at spliters answer below.

If it were to be possible, it would look something like...

ul li:last-child+li {...}

But this doesn't work, because + will select the immediate sibling after last-child (which is nothing, of course). There is no immediate previous selector.

There are different ways of achieving this with jQuery, the most performant would be...

var lastItems = $("#list li");
lastItems.slice(lastItems.length - 2).addClass("whatever");

http://jsfiddle.net/qkzdJ/

:last-child,
:nth-last-child(2) {
  ruleset
}

will play as well.

It is possible with CSS3. Consider the markup:

<ul>
    <li><a href="">First item</a></li>
    <li>Second item</li>
    <li><a href="">Test</a></li>
    <li><a href="">Test</a></li>
    <li><a href="">Pre-last item</a></li>
    <li><a href="">Last item</a></li>
</ul>

To choose the last two LI elements you do:

ul > li:nth-last-of-type(-n+2) {
    background: green;
}

Works in all contemporary browsers including IE9, but excluding IE8 and below. To add support for those browsers, you might consider using Selectivizr.js

For me it was this: li:not(:nth-last-child(-n+2))