By Shad Super in Questions —

How Can I Identify and Fix Dynamic Content Shifts on Mobile Pages to Resolve the "CLS Issue: More Than 0.1 (Mobile)" Problem?

Summary

The Cumulative Layout Shift (CLS) problem refers to visual instability caused by elements shifting during page load. A high CLS score, such as more than 0.1, indicates a poor user experience. Identifying and fixing the dynamic content shifts can involve steps like avoiding or minimizing the use of dynamically injected content, making sure ad elements have a reserved space, and preloading key web fonts. Here's a detailed guide on how to resolve the "CLS issue: more than 0.1 (mobile)" problem.

Identifying Layout Shifts

Chrome DevTools

The Layout Shift Regions tool in Chrome DevTools helps visualize unstable elements. Through the Performance panel, you can record a page load and view layout shift scores and details [Chrome DevTools for Performance Analysis, 2022].

WebPageTest

WebPageTest.org provides a filmstrip view that indicates layout shifts during page load [Optimizing Cumulative Layout Shift, 2020].

Fixing Layout Shifts

Dynamically Injected Content

Avoid or minimize the use of dynamically injected content, especially if the user interaction isn't required. It's better to have reserve space for the content upfront with CSS aspect-ratio boxes [Avoid layout shifts with CSS aspect ratio, 2022].

Ads, Embeds, and Iframes

Make sure these elements have a reserved space in the viewport to prevent content from shifting when they load. Use the `width` and `height` attributes for iframes and embeds [Ads, embeds, and iframes without dimensions, 2022].

Web Fonts

Web fonts can cause significant layout shifts. Preloading key web fonts can prevent this issue. Use `font-display: optional` or `font-display: swap` for decorative fonts to prevent layout shift [Web fonts causing FOUT/FOIT, 2022].

Animations

Use the transform CSS property for animations as it doesn't trigger layout changes and won't contribute to CLS [Animations, 2022].

Conclusion

Improving Cumulative Layout Shift performance involves a strategic approach to preventing and minimizing dynamic content shifts. Using tools like Chrome DevTools and WebPageTest.org can help identify instability issues. Solutions typically involve reserving space for dynamic elements, preloading web fonts, and using the correct CSS properties for animations.

References