Frontend Fundamentals: HTML, CSS, and Responsive Styling Questions

Core web-platform implementation skills: semantic HTML and document structure, native controls versus ARIA-patched divs (button versus link), accessible markup (labels, headings, landmarks, image alt text, icon-only buttons, keyboard operability, skip links, ARIA basics, focus styles), the CSS box model, cascade and specificity (including cascade layers and taming !important), selector matching cost, display types, positioning (static, relative, absolute, fixed, sticky) and stacking contexts and z-index, flexbox and grid layout (including subgrid and masonry options), units and fluid sizing (rem, clamp, viewport units including dynamic viewport units), the viewport meta tag, media queries, mobile-first breakpoints and how to choose them, container queries, responsive images (srcset, sizes, picture, aspect-ratio), touch target sizing, right-to-left and long-text layouts, custom properties and light/dark theming, and CSS organization (BEM, CSS Modules, utility-first, Sass). Includes debugging layout bugs, progressive enhancement, @supports and cross-engine CSS fallbacks. Performance measurement, building full interactive widgets and form flows, design-system governance, WCAG audit strategy, design handoff, visual regression testing and cross-browser test coverage are covered elsewhere.