Performance
How to measure and improve real-world web performance — Core Web Vitals (LCP, INP, CLS), bundle analysis, profiling, perceived performance tricks, and the hydration cost that nobody warned you about.
Accessibility
How to build interfaces that work for keyboard users, screen reader users, low-vision users, and people on shaky networks or unfamiliar devices. WCAG, ARIA (and when not to use it), focus management, contrast, semantic HTML — and why "do it from the start" is the only realistic strategy.