CSS (Cascading Style Sheets) is a language used to style and format web pages.

CSS, or Cascading Style Sheets, is a core technology in web development that controls the appearance and layout of HTML elements on a webpage. While HTML provides the structure and content, CSS is responsible for the visual presentation—such as colors, fonts, spacing, and positioning.

Key Features of CSS 

• Separation of Content and Design: CSS allows developers to keep the content (HTML) separate from the design, making websites easier to maintain and update.
• Selectors and Properties: CSS uses selectors to target HTML elements and properties to define how those elements should look.

For example:

p {
color: green;
font-size: 16px;
}

• Responsive Design: CSS enables web pages to adapt to different screen sizes and devices using techniques like media queries.
• Styling States: With pseudo-classes (like ‎`:hover`), CSS can style elements based on user interaction or their state.

Example 

Here’s a simple example that changes the color of a button when you hover over it:

button:hover {
  color: blue;
}

/* Syntax */
selector:pseudo-class {
  property: value;
}
/* Any button over which the user's pointer is hovering */
button:hover {
  color: blue;
}