Why it matters
Large DOM trees make style recalculation, layout and every interaction slower and increase memory.
How to fix it
Paginate or virtualize long lists, remove hidden duplicate markup (e.g. separate mobile/desktop menus), and render off-screen sections lazily with content-visibility: auto.
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.
images-missing-dimensionsImages without width/height or aspect-ratiorender-blockingRender-blocking resources delay first paintno-text-compressionText resources are served uncompressedcache-headersHashed static assets are not cached long-termthird-party-heavyHeavy third-party footprintbfcache-blockedPage is not eligible for the back/forward cachelighthouse-score-lowLighthouse performance score is lowlighthouse-auditLighthouse flagged an opportunity