Summary  
This chapter introduces CSS as a way to control the appearance of HTML elements by using selectors and declaration blocks composed of property–value pairs to define colors, spacing, fonts, alignment, and layout without altering document structure.

General domain of usage  
Web development

HTML defines the structure and content of a web page.
 CSS defines how that content is presented.

While HTML organizes elements such as headings, paragraphs, and images, **CSS controls** their **appearance**, including colors, spacing, fonts, alignment, and layout.

Together, HTML and CSS form the foundation of modern web development.

CSS stands for Cascading Style Sheets.
It is a stylesheet language used to describe how HTML elements should be displayed in a browser.

Definition

With CSS, you can:
- Change text and background colors;
- Adjust spacing between elements;
- Control fonts and typography;
- Create layouts;
- Add visual effects.

CSS does not change the structure of a document.
 It controls how that structure looks.

## Basic CSS Syntax
A CSS rule consists of a selector and a declaration block.<br>
Example:
```css
p {
  color: purple;
  background-color: green;
}
```
Explanation:
- `p` is the selector. It targets all `<p>` elements;
- `color: purple;` sets the text color;
- `background-color: green;` sets the background color.

Each declaration follows this format: `property: value;`

You will explore selectors, properties, and values in detail in upcoming chapters.

Style web pages using CSS to control layout, spacing, colors, and typography. Work with selectors, the box model, and Flexbox to build structured layouts. Create modern UI components using backgrounds, fonts, and visual effects.

What CSS Is and Why It Matters

What Is CSS?

Basic CSS Syntax