CSS Custom Properties

React Hooks are functions (like `useState`, `useEffect`, `useMemo`, `useCallback`) that let you use state, side effects, and other React features inside functional components without writing classes. Introduced in React 16.8, they fundamentally changed how React applications are structured by enabling logic reuse through custom hooks. Hooks must follow two rules: they can only be called at the top level of a component, and only inside React function components or other hooks.

A toast notification is a small, non-intrusive message that appears briefly on screen — usually at the top or bottom — to provide feedback about an action without interrupting the user's workflow. Unlike modals, toasts auto-dismiss after a few seconds and don't require user interaction. They are commonly used to confirm saves, report errors, or show status updates. Accessible implementations include ARIA live regions so screen readers announce the message.

Dart is the programming language created by Google and used as the sole language for Flutter development. It features a sound type system, null safety, async/await support, and compiles both ahead-of-time (AOT) for production performance and just-in-time (JIT) for fast development cycles with hot reload. Dart's syntax feels familiar to developers coming from JavaScript, TypeScript, Java, or Kotlin, making the transition to Flutter relatively smooth.

CSS Animation uses `@keyframes` rules and the `animation` property to create complex, multi-step animations entirely in CSS without JavaScript. Combined with CSS transitions for simple state changes, these tools handle most UI animation needs performantly since browsers can optimize them on the GPU compositor thread. Properties like `transform` and `opacity` are particularly efficient to animate because they don't trigger layout recalculations or repaints.

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.

JSX (JavaScript XML) is a syntax extension for JavaScript used primarily in React that lets you write HTML-like markup directly within your JavaScript code. It gets transpiled by tools like Babel or SWC into regular `React.createElement()` calls before reaching the browser. JSX supports embedding dynamic expressions with curly braces, conditional rendering, and mapping over arrays, making it a powerful and intuitive way to describe UI structures declaratively.