Milica Mihajlija takes on CSS performance and says the most straightforward approach is to keep it small. Compressing files can significantly improve speed, but removing unused code can too. Other methods include using efficient CSS animations and avoiding invisible text during font loading.
“CSS is critical to loading pages and a delightful user experience. While we often might prioritize other assets (such as script or imagery) as more impactful, we shouldn’t forget CSS.”