Pseudo elements

Summary

Selectors like `::before` and `::after` that let you insert styled content into an element without adding it to the HTML. They are ideal for decorative presentation, but important information should generally remain in semantic HTML so it is available to assistive technologies and other consumers.

• 1Add a decorative icon or quote mark using `::before`/`::after`. Test the result on both a successful path and an invalid or unexpected input.
• 2Build a custom checkbox or tooltip arrow using pseudo-elements. Keep the first version small, then add one improvement after the core behavior works.
• 3Learn the required `content` property — without it, pseudo-elements won't render.