CSS rules are made up of selectors and declarations. A selector is used to target an HTML element, while declarations contain rule properties and values that are applied to the targeted element.

This question leads to one of the most important ideas behind CSS: The selector, so named because it’s the way we “select” the HTML we want to style.

Understanding how browsers parse CSS and render websites is an important first step towards writing more efficient code. In this first piece on efficient CSS, we look at selectors, how the browser ...