What's the Difference Between CSS Pseudo-Classes and Pseudo-Elements?

Difference between CSS Pseudo-Classes and Pseudo-Elements

Overview

CSS pseudo-classes and pseudo-elements are both used to enhance selector specificity, but they serve distinct roles in styling.

Pseudo-Classes

Pseudo-classes are used to target elements based on their state or behavior. They begin with a colon (:) followed by a keyword or value in parentheses. Pseudo-classes can include information that cannot be derived from the document structure, such as:

• :hover - On hover
• :active - When clicked
• :target - Element with a specific ID matching the hash in the URL

Pseudo-Elements

Pseudo-elements create virtual elements that are not present in the document, but can be styled and manipulated. They begin with double colons (::) followed by a keyword. Pseudo-elements provide access to content and features otherwise unavailable, such as:

• ::first-line - First line of text
• ::before - Content inserted before an element
• ::after - Content inserted after an element

Key Differences

Feature	Pseudo-Class	Pseudo-Element
Purpose	Selects elements	Creates virtual elements
Syntax	element:keyword	element::keyword
Example	a:hover	p::before
Content Manipulation	N/A	Supports content generation and modification
Multiple Instances	Multiple allowed	Only one per selector

Example Usage

To apply a background color to elements with a class of "important" when hovered over:

.important:hover {
  background-color: #FF0000;
}

To add a language tag after quotes on the page:

q::after {
  content: " (Language: " attr(lang) ")";
}

Summary

Pseudo-classes are used for selecting elements based on their context or behavior, while pseudo-elements create virtual elements with accessible content and styling options. Understanding this distinction is essential for effective use of these advanced CSS techniques.

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