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CSS CSS Foundations Advanced Selectors Pseudo-Classes: :nth-child

I figured out the problem with my code

Q: Create a new rule that targets the first 4 list items only. Set the font weight to bold.

My first answer:

li:nth-child(4-n) { font-weight: bold; }

Correct answer: li:nth-child(-n+4) { font-weight: bold; }

The browser only understands :nth-child(an+b) pseudo-class's of that form, not of the form :nth-child(b+an). Thus the :nth-child pseudo-class has order-sensitive arguments!