There’s one final piece of the performance puzzle that has less to do with page download speed, and more to do with on-site page performance—and it's just as important. It doesn't matter if your site loads instantly if it jitters and chugs whenever someone tries to use it. In fact, that’s even worse. Load speed is only annoying at first, but a laggy page is annoying throughout the entire browsing experience.
How can you keep your page snappy even after it’s been loaded? It’s all about limiting the amount of processing work the computer needs to do. Primarily, this means limiting animations and UI flourishes:Don’t go heavy on animations. Animations require a lot of processing and graphics power, and can cause serious lag.
Avoid animating images as much as possible. You can sprinkle them in there, but don't go overboard. Animations require a lot of power, and animating images requires exponentially more power! Browsers have a hard time doing this type of work in bulk — especially on mobile devices.Be careful about adding too many background gradients, box shadows, and text shadows. These are forms of “pseudo-images” that are equally as intensive for the browser to animate.