UTC vs local time, offsets vs zones, DST edge cases, ISO 8601/RFC 3339, DB column types, and sane patterns in JS/Python/SQL. How to store, compare, schedule, and display time without pain.
A practical mental model of tasks vs microtasks, when the browser renders, and patterns to keep 60fps: rAF, chunking, debouncing, and avoiding microtask traps.
Low‑effort, high‑impact a11y fixes: alt text, semantic HTML & landmarks, color contrast (and non‑color cues), keyboard navigation & focus, and form labels/errors—with copy‑paste examples.