A CSS selector is the first part of a CSS Rule. It is a pattern of elements and other terms that tell the browser which HTML elements should be selected to have the CSS property values inside the rule applied to them.

Which is an example of a class selector?

A class selector looks just like an element selector, but instead of using names that are tied to the names of HTML elements, you make up the name and then you prefix it with a dot (.). For instance: . red { }

What are simple selectors in CSS?

A simple selector is either a type selector or universal selector followed immediately by zero or more attribute selectors, ID selectors, or pseudo-classes, in any order. The simple selector matches if all of its components match. Note: the terminology used here in CSS 2.2 is different from what is used in CSS3.