Why it matters
Stylesheets are render-blocking: the browser paints nothing until they arrive and parse.
How to fix it
Remove unused CSS (Tailwind v4 only emits used utilities; check @source globs and safelists), split route CSS, and drop CSS frameworks you override.
More performance rules
void perf reports 25 rules in this category. Core Web Vitals and bytes: LCP, CLS, TBT, TTFB, JavaScript, CSS, fonts, images, caching and compression, measured as the median of several runs on a throttled mobile and a desktop profile.
ttfb-slowServer response (TTFB) is slowfcp-slowFirst Contentful Paint is slowtbt-highMain thread is blocked by long tasks during loadjs-budgetFirst-load JavaScript exceeds the budgetfont-budgetWeb font transfer exceeds the budgettoo-many-fontsToo many font files are downloadedimage-budgetImage transfer exceeds the budgettoo-many-requestsPage makes many requests