CSS Custom Properties

Accessibility (often abbreviated a11y) is the practice of designing and building websites and apps so they can be used by everyone, including people with visual, motor, auditory, or cognitive disabilities. This involves proper semantic markup, keyboard navigation support, sufficient color contrast, and screen reader compatibility. Beyond being an ethical responsibility, accessibility is increasingly a legal requirement in many jurisdictions.

React's Context API provides a way to pass data through the component tree without manually threading props through every intermediate level. You create a context with `createContext`, wrap a subtree with a `Provider`, and consume the value anywhere below with `useContext`. It's ideal for global concerns like themes, authentication state, or locale, but should be used judiciously since any change to context value re-renders all consuming components.

A modal (or modal dialog) is a UI element that overlays the main content to demand user attention and interaction before they can return to the underlying page. Modals are used for confirmations, forms, alerts, and content previews. Proper implementation requires focus trapping, keyboard accessibility (Escape to close), and preventing background scroll — making accessible modals more complex than they appear.

CI/CD (Continuous Integration / Continuous Deployment) is a set of practices that automate building, testing, and deploying code every time a developer pushes changes. Continuous Integration merges code into a shared branch frequently and runs automated tests, while Continuous Deployment automatically releases validated changes to production. Together they form the backbone of modern software delivery, reducing manual errors and accelerating release cycles.

Color contrast is the measurable difference in luminance between foreground text (or UI elements) and their background. WCAG guidelines require a minimum contrast ratio of 4.5:1 for normal text and 3:1 for large text to ensure readability for users with visual impairments. Tools like Chrome DevTools, Stark, and WebAIM's contrast checker help developers verify compliance during development.

Event-driven architecture (EDA) is a software design pattern where components communicate by producing and consuming events rather than making direct synchronous calls. When something happens — a user signs up, an order is placed — an event is emitted, and any number of subscribers can react independently. This decoupling enables highly scalable, loosely coupled systems where new automations can be added without modifying existing services.