Accessibility

React Server Components (RSC) are components that render exclusively on the server and send only their HTML output to the client, with zero JavaScript bundle impact. They can directly access databases, file systems, and backend services without API endpoints. Combined with Client Components (marked with `'use client'`), RSC enables a hybrid architecture where interactive parts ship JavaScript while static or data-heavy parts remain server-only. Next.js App Router uses RSC as its default component model.

Server-Side Rendering (SSR) is a technique where web pages are rendered to HTML on the server for each request, rather than relying on client-side JavaScript to build the page in the browser. SSR provides faster initial page loads and better SEO since search engines receive complete HTML content. Modern SSR in frameworks like Next.js supports streaming, allowing the server to progressively send HTML chunks as they become ready rather than waiting for the entire page to render.

BEM (Block Element Modifier) is a CSS naming convention that structures class names as `.block__element--modifier` to create clear, predictable relationships between HTML and CSS. For example, `.card__title--highlighted` identifies a highlighted title element within a card block. While modern tooling like CSS Modules and utility frameworks have reduced BEM's necessity, it remains widely used in large codebases and design systems where explicit naming conventions aid team coordination.

Tailwind CSS is a utility-first CSS framework that provides low-level utility classes like `flex`, `pt-4`, `text-center`, and `bg-blue-500` to build designs directly in your markup. Instead of writing custom CSS, you compose pre-built classes to create any design, which results in smaller final CSS bundles thanks to automatic purging of unused styles. Its configuration file allows full customization of the design system including colors, spacing, breakpoints, and typography.

Progressive enhancement is a web development strategy that starts with a baseline of functional HTML content accessible to all browsers, then layers on CSS styling and JavaScript interactivity for more capable environments. This approach ensures that core functionality works everywhere, while users with modern browsers get a richer experience. It contrasts with graceful degradation, which starts with the full experience and tries to handle failures.

Shadow DOM is a browser API that allows you to attach a hidden, encapsulated DOM tree to an element, isolating its styles and markup from the rest of the page. This means CSS defined inside a Shadow DOM won't leak out, and external styles won't bleed in. It's the core technology behind Web Components and is used by frameworks to achieve true style encapsulation without CSS naming conventions or tooling.