35 checks in Core Web Vitals & Performance. Automated Its subsection has a live automated checker in the engine.
| ID | Check | Passes when |
|---|---|---|
| 4.3.01 | Extract total CSS payload size | < 150KB compressed |
| 4.3.02 | Extract uncompressed CSS size | < 500KB |
| 4.3.03 | Identify number of CSS files requested | ≤ 5 |
| 4.3.04 | Validate primary CSS served as single main bundle | Consolidated |
| 4.3.05 | Validate usage of critical CSS for above-the-fold content | Implemented |
| 4.3.06 | Validate non-critical CSS is loaded async/deferred | Yes |
| 4.3.07 | Detect render-blocking CSS in <head> | Minimized |
| 4.3.08 | Validate media attributes on non-screen stylesheets | Correct |
| 4.3.09 | Validate CSS is minified | Yes |
| 4.3.10 | Validate removal of unused CSS (coverage < 30% unused) | Efficient |
| 4.3.11 | Detect large frameworks (e.g., Bootstrap/Tailwind) shipped mostly unused | Avoid waste |
| 4.3.12 | Validate logical layering of CSS (base → layout → components → utilities) | Structured |
| 4.3.13 | Detect overly-specific selectors causing bloat | Minimized |
| 4.3.14 | Detect !important overuse | Minimal |
| 4.3.15 | Validate CLS-related CSS is stable (fixed heights, aspect-ratio, etc.) | Stable |
| 4.3.16 | Validate responsive breakpoints are consistent and documented | Clean breakpoints |
| 4.3.17 | Validate mobile-first CSS strategy | Yes |
| 4.3.18 | Validate usage of modern layout (flexbox, grid) | Modern |
| 4.3.19 | Validate avoidance of heavy legacy layout (float-based) | Minimal legacy |
| 4.3.20 | Validate color variables (CSS custom properties) for theme consistency | Implemented |
| 4.3.21 | Validate dark-mode support where relevant | Supported or intentionally absent |
| 4.3.22 | Validate font-face declarations optimized (WOFF2, swap) | Optimized |
| 4.3.23 | Validate no blocking @import in CSS | None |
| 4.3.24 | Validate no CSS loaded via JS for critical path | Avoided |
| 4.3.25 | Validate print styles separate and lightweight | Optimized |
| 4.3.26 | Detect unnecessary animation/transition definitions | Minimal |
| 4.3.27 | Validate no layout thrashing from CSS animations | Stable |
| 4.3.28 | Validate prefers-reduced-motion support | Implemented |
| 4.3.29 | Validate use of logical properties (margin-inline, etc.) for locale support | Modern |
| 4.3.30 | Detect duplicated rules across CSS files | Deduplicated |
| 4.3.31 | Validate CSS specificity manageable (no deep chains) | Maintainable |
| 4.3.32 | Validate CSS does not delay LCP | Minimal impact |
| 4.3.33 | Validate sass/less/postcss pipeline output is clean | No debug leftovers |
| 4.3.34 | Validate component-level CSS scoping used (CSS modules, scoped, etc.) | Used where appropriate |
| 4.3.35 | Compute CSS optimization & render-path composite score | >= 90% |
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