Element Selector
This selects an HTML element using the element's name (or tag), such as h1, p, body, div, etc.
Universal & Grouping Selector
A universal selector selects all of the HTML elements using an *. A grouping selector can be used when multiple elements have the same styling. The selectors are all listed together and separated by commas to minimalize the code.
class Selector
This uses an HTML element's class attribute - which is created and assigned by the user - to specify the element that will be styled. A class selector isn't unique, so it can be reused. A class is represented by a period, followed by the class name.
id Selector
This uses an HTML element's id attribute - which is created and assigned by the user - to specify the element that will be styled. All id's are unique, so they will only be used once. An id is represented by a #, followed by the id name.