CLS — Cumulative Layout Shift — measures content jumping around (that annoying moment a button hops just as you tap). Many people assume it's purely a page-load problem you can ignore once things settle.
The correction: Google now measures shifts across the whole time a visitor is on the page, not just the first few seconds. A cookie banner sliding in, a lazy-loaded ad, or an "accept" popup can ding your score minutes later.
How to check:
— Open Chrome DevTools, go to the Performance tab, record while you interact.
— Watch for blue "Layout Shift" markers in the timeline.
— Note what triggered each one.
Try this: scroll your own page slowly and watch for anything that nudges content. Reserve space for it. This one's about patience, not just speed.
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Myth: layout shift only happens while loading
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