Browser cache - Sometimes the browser is still loading the old CSS file. A hard refresh (Ctrl + F5) usually fixes it. Wrong file linked - Double-check if your HTML is actually linked to the correct CSS file. Specificity issues - Another CSS rule might be overriding your changes.
Introduction Have you heard of the @starting-style at-rule? It's an interesting new tool that lets us use CSS transitions for enter animations. For example, let's suppose we have some UI where elements get added dynamically to the page, and we want them to fade in: When you click the "Add Element" button, a new purple square is generated and added to the page, and a CSS keyframe animation fades it in over 1 second.