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.A single line of CSS consists of two things, a property and a value. Properties are the things that you want to style, and values are the things that you want to apply to those properties.
Selector links The two selectors class selector .planet and id selector of #planet
Properties linkThe two properties are border: red 2px solid; and font-family: helvetica;
In this documentation I have learned CSS selectors and properties, which enable us to target particular HTML elements, and more of the CSS rules.