React Hooks

In Flutter, the widget tree is the hierarchical structure of nested widgets that defines the entire UI of an application. Everything in Flutter is a widget — from layout structures like `Column` and `Row` to styling wrappers like `Padding` and `Theme` to interactive elements like `GestureDetector`. Flutter maintains three parallel trees (widget, element, and render object) that work together to efficiently rebuild only the parts of the UI that actually changed when state updates.

Dark mode is a UI color scheme that uses light-colored text and elements on a dark background. It reduces eye strain in low-light environments, can save battery on OLED screens, and has become an expected feature in modern applications. Implementation typically involves CSS custom properties or design tokens that switch between light and dark theme values, often respecting the user's system-level preference via the `prefers-color-scheme` media query.

Redux is a predictable state management library that stores the entire application state in a single immutable store, updated exclusively through dispatched actions and pure reducer functions. Redux Toolkit (RTK) is now the recommended way to use Redux, dramatically reducing boilerplate with utilities like `createSlice` and `createAsyncThunk`. While Redux remains popular in large enterprise applications that benefit from strict unidirectional data flow and time-travel debugging, lighter alternatives like Zustand have gained ground for simpler use cases.

CSS Grid is a two-dimensional layout system that lets you define rows and columns simultaneously, making it ideal for complex page layouts. Unlike Flexbox which works in one axis at a time, Grid allows you to place items precisely in both horizontal and vertical directions using named areas or line numbers. Features like `grid-template-areas`, `auto-fill`, and `minmax()` make it possible to create responsive layouts with minimal code.

Design tokens are the smallest units of a design system — named values representing colors, spacing, typography, border radii, and other visual properties. They act as a single source of truth that can be translated into platform-specific formats (CSS variables, Swift constants, XML resources). By changing token values in one place, you can update the look and feel of an entire application across multiple platforms simultaneously.

Next.js is a full-stack React framework by Vercel that provides server-side rendering, static site generation, API routes, file-based routing, and built-in optimizations out of the box. Its App Router (introduced in v13) uses React Server Components by default, enabling a new paradigm of server-first rendering with selective client-side interactivity. Next.js has become the de facto standard for production React applications due to its performance optimizations, developer experience, and deployment flexibility.