Trace a detached preview from its DOM node to an application Map, repair cleanup, and verify repeated open-and-close cycles with heap snapshots.
Record one slow click in Chrome's Performance panel, read the Bottom-up tab by self time, fix the function it points at, and record again to prove the fix worked.
Reproduce a nested-container breakpoint failure, select the intended named ancestor, and verify the repair at a fixed viewport and at its boundary.
Put an old stylesheet in the first layer so your new rules win without touching the old file or raising specificity.
Keep spinners and fades, replace slides and smooth scrolling, and check both settings in Chrome.
Compute size-adjust and the vertical overrides from the font files, build the fallback face, and measure the layout shift before and after.
Measure the real slot width at each breakpoint, write sizes from it, and check which file loads at each screen density.
Mark the first-screen rules once, split the stylesheet in the build, and confirm the rest loads without blocking.
Use one token file with light-dark(), add a saved toggle that does not flash, and check the colours in both themes.
Switch brands with a data attribute, and avoid the derived-token trap that freezes hover colours on the wrong value.
Use a native dialog, animate it with CSS only, and check focus, Tab, Escape and reduced motion by keyboard.
Record coverage in Chrome DevTools, test the states that hide rules, and remove dead CSS in small, reversible steps.