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CSS-in-JS Runtime Overhead Hurts Core Web Vitals

7/10 High

CSS-in-JS libraries like Styled Components run JavaScript in the browser to hash class names and inject styles dynamically, causing style recalculations on every injection. This significantly degrades LCP, FCP, and INP metrics.

Next.jsStyled ComponentsReact
Category
performance
Workaround
solid
Stage
build
Freshness
persistent
Scope
framework
Recurring
Yes

Sources

Collection History

Query: “What are the most common pain points with Next.js in 2025?”3/27/2026

CSS-in-JS libraries like Styled Components run JavaScript on the client to hash class names and inject styles into the DOM. Each injection causes browser style recalculation for the entire page, significantly hurting LCP, FCP, and INP.

Created: 3/27/2026Updated: 3/27/2026