Perceived performance is not only about fast page loads and delivering the content as early as possible. It is also about all the interactions happening on an already loaded page. Even some of the most popular UI patterns can be a cause of frustration. Understanding what is happening under the browser’s hood can help you delight users with a smooth experience and avoid potential performance issues. Let’s demystify the rendering process and look into possible optimisations in order to achieve the best experience after the initial page load.