A CSS rule set contains two blocks.
Selector:
The HTML element to be styled is specified by a selector.
Declaration Block:
One or more declarations containing a property name and value separated by a semicolon are included in the declaration block.
Property:
The type of attribute of the HTML element is known as property. For example, color, border, etc.
Value:
CSS properties are assigned with certain values.
Syntax:
Selector{Property1: value1; Property2: value2; ..........;}