CSS

CSS is not only decoration. It is the rule system that turns document structure into responsive layout, visual hierarchy, interaction states, theming, and measurable rendering cost. Strong interview answers connect the cascade, layout algorithms, architecture choices, and browser work such as style calculation, layout, paint, and compositing.

Child sections cover core concepts, layout systems, styling architecture, modern CSS features, and performance. HTML defines behavior; CSS defines presentation without replacing semantics.

On interviews: explain how a style rule wins in the cascade and how layout choice affects maintainability — not just which property centers a div.

Common pitfalls: specificity wars, viewport-only responsive design, and treating CSS as a pile of overrides instead of a system.

Checklist:

• Connect cascade, layout, architecture, and rendering cost.
• Use child topics for depth on each area.
• Prefer predictable ownership over one-off overrides.
• Measure performance when CSS delivery blocks paint.