Despite the super fun sounding name, magic numbers are a bad thing. It is an old school programming term for "unnamed numerical constant". As in, just some number plunked into the code that is probably vital to things working correctly but are very difficult for anyone not intimately familiar with the code to understand what it is for. CSS is loaded with unnamed numerical constants, but they are usually paired with properties and in the context of a selector so there is little mystery. There are magic numbers in CSS though, and they are still bad.