CSS (Cascading Style Sheets) is a style sheet language used for describing the look and formatting of a document written in HTML or XML. It's commonly used to style web pages and interfaces written in HTML and XHTML. CSS is designed to enable the separation of document content from document presentation, including aspects like layout, colors, and fonts. This separation can improve content accessibility and provide more flexibility and control in the specification of presentation characteristics.

Here are some key concepts and examples on how to style your website.

Key Concepts

Selectors: These are used to select and manipulate HTML elements. They're used to "find" HTML elements based on their id, class, type, attribute, and more.

Properties: After you've selected an HTML element with a selector, you can define properties for it. Each property has a name and a value, separated by a colon. Each declaration ends with a semicolon.

Declaration Block: For each selector, there can be a declaration block which includes one or more declarations separated by semicolons.

Here's the syntax:

selector {
property1: value1;
property2: value2;
...
}

Practical

Let's go step by step on how to use CSS in a practical scenario. We will create a simple webpage with HTML and style it with CSS.