Craft

Spacing & alignment

The 4px grid, concentric radius, and why Spotify's play button isn't centred

Colour systems

HSL's lightness axis lies. OKLCH fixes it.

Layout patterns

Most JS layout reads could be CSS. Plus the four states every component ships without.

Mobile resilience

Your CSS doesn't know about the notch, the home bar, or the keyboard

Interaction details

Where does focus go when the dialog closes? Can you hit that icon on a phone?

Accessibility

Same five bugs in every audit: div buttons, missing labels, broken headings

Forms

Missing labels, broken autocomplete, punitive validation. A respect problem.

Navigation & feedback

Right click a button. If 'Open in new tab' appears, it should be a link.

Microcopy

The four words on a button matter more than the four hundred on the page

Performance details

Did the paragraph jump when the hero loaded? That's CLS. It's preventable.

Polish: the last 5%

None of these survive an A/B test alone. Together, they're why users say 'premium'.