A CSS rule is interpreted by the browser and then applied to the corresponding elements in our HTML document. A style rule is composed of three parts:
Selector − is used to “find” (or select) HTML elements based on their element name, id, class, attribute, and more.
Property − is a type of style of the CSS. It could be color, border, background, font, display, text alignment, margins, line spacing, etc.
Value − is assigned to properties. For example, background-color property can have a value of either red or green.