CSS is short for Cascading Style Sheets. But what exactly is this Cascade, and how does it work? What are Origins? How do you calculate Specificity? And where do those new Cascade Layers you might have heard of fit in? And oh, what exactly happens when you use an !important somewhere? In this insightful talk, we’ll take a look under the hood of browsers, and detail how they determine which CSS declarations to apply and which not.