Lecture Notes on CSS Pseudo Elements: Before and After

Introduction

• Pseudo elements are used to add style without extra markup.
• Commonly misunderstood, especially regarding their functionality.
• This video is part of a three-part series on pseudo elements.
  • Part 1: Overview of how they work.
  • Part 2: Exploring the content property.
  • Part 3: Using pseudo elements for design enhancements.

Understanding Pseudo Elements

• Pseudo elements are written as ::before and ::after (double colon) in CSS.
• The original specification used a single colon, but CSS3 standardized it to double colons to distinguish from pseudo classes (e.g., :hover).
• Browsers still support the old syntax (single colon) for backward compatibility.

Implementing Pseudo Elements

• Basic syntax example: p::before { content: ''; background: red; display: block; position: absolute; top: 0; left: 0; height: 10px; width: 10px; }
• Key Point: The content property is essential. Without it, the pseudo element defaults to none and does not render.

Misconceptions

• Common Misconception: ::before and ::after insert elements before or after the paragraph itself.
  • Reality: They insert content before or after the actual content inside the paragraph or div.
• Example of inspecting in developer tools:
  • Pseudo elements appear within the content structure, not as separate elements.

Limitations with Images

• Pseudo elements do not work on replaced elements like <img>.
• An <img> tag cannot have ::before or ::after because it does not follow the standard content model of CSS.
• Images have their content defined by their src attribute, making them behave differently.

Styling Pseudo Elements

• Pseudo elements can be styled independently: p::before { content: 'Hello'; color: white; background: red; display: inline; } p::after { content: 'Goodbye'; color: white; background: blue; display: inline; }
• They can be set to display as inline or block.

Use Cases

• Pseudo elements can be used for design elements without adding additional markup (e.g., empty <div>s for design).
• The content property allows for creative styling options that enhance design without cluttering HTML.

Conclusion

• Understanding how ::before and ::after work is crucial to effectively using them in web design.
• Future videos will delve deeper into the content property and creative applications.
• Encourage viewers to ask questions and provide support through Patreon.