Why INP made CSS performance urgent

Michael Hladky joins the pod to explain how CSS performance improvements like content-visibility, CSS containment, contain layout, and contain paint can dramatically outperform JavaScript virtual scrolling. The conversation explores virtual scrolling, large DOM performance, and how layout and paint work inside the browser rendering pipeline, including recalculate styles and their impact on INP Interaction to Next Paint. Michael shares real-world examples of frontend performance optimization, discusses cross-browser CSS support including Safari content-visibility, and explains why web performance issues tied to rendering are often misunderstood and overlooked.

Links

LinkedIn: https://www.linkedin.com/in/michael-hladky-519340148/
GitHub: https://github.com/BioPhoton
X: https://x.com/Michael_Hladky

Resources

Conference link: https://push-based.io/event/perfnow-2025-michael-hladky-zero-js-virtual-scrolling-css
Conference resource: https://github.com/push-based/css-contain-and-content-visibility-research

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Chapters

00:00 Introduction to CSS Performance and Virtual Scrolling
01:20 Why Interaction to Next Paint (INP) Changed Everything
03:00 The Real Cost of Layout and Paint
05:10 Why Large DOMs Break Performance
06:45 How CSS Containment Works
08:30 Contain Layout vs Contain Paint Explained
10:40 When Containment Breaks Your UI
12:20 Introducing Content Visibility
14:10 CSS Content Visibility vs JavaScript Virtual Scrolling
16:40 Why CSS Skips Recalculate Styles Entirely
18:50 Real Performance Gains on Desktop and Mobile
20:40 Cross-Browser Support Including Safari
22:10 Common Pitfalls and Flickering Issues
24:10 How to Measure Layout and Paint Performance
26:10 Why Frameworks Should Use This by Default
28:00 Design Systems and Low-Hanging Performance Wins
30:10 The Biggest CSS Performance Misconception
32:00 Final Takeaways on Frontend Performance