- Add package.json with ESLint v9, typescript-eslint, eslint-plugin-react,
eslint-plugin-react-hooks, eslint-config-prettier, Prettier, and TypeScript
as devDependencies; includes lint, format, and format:check npm scripts
- Add eslint.config.js (flat config) with TypeScript recommended rules,
React + React Hooks plugin rules, and prettier conflict suppression
- Add tsconfig.json with strict: true, ES2020 target, DOM libs, react-jsx
- Add .prettierrc with single quotes, 2-space indent, ES5 trailing commas
- Update CLAUDE.md to document new tooling and commands
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
- Add styles.css with mobile-first responsive design (Flexbox/Grid)
- Three breakpoints: mobile (320px+), tablet (768px+), desktop (1024px+)
- All interactive elements meet 44x44px minimum touch target size
- WCAG AA color contrast: text #1a1a1a on white (~17:1), buttons #fff on #1565c0 (~5.85:1), error #c62828 on white (~5.6:1)
- Clear visual hierarchy: h1 > h2 > body text, prominent result area, red error styling
- Link styles.css from index.html
- Update CLAUDE.md project structure to include styles.css
Create semantic HTML5 structure for calculator interface:
- index.html: two labeled number inputs, four operation buttons,
calculate/clear buttons, result <output>, and error <p role=alert>
with aria-live regions for screen-reader accessibility
- CLAUDE.md: updated project structure and architecture notes
