CSS selector all but the first child

There is no selector of all but the first child. Cristian’s answer is perfect to get what you want and is the simplest.

But there is also a negation selector :not(), which combined with the :first-child selector can produce the effect you are looking for.

The code would look like this:

li:not(:first-child) { font-weight: bold; }

I think this is available in all browsers. Even Internet Explorer.