Flutter

GitOps is an operational model where Git repositories serve as the single source of truth for both application code and infrastructure configuration. Automated agents like ArgoCD or Flux continuously monitor the repo and synchronize the live environment to match the declared state. Every change goes through pull requests, providing a full audit trail and enabling rollbacks by simply reverting a commit.

CSS Custom Properties (also called CSS Variables) let you define reusable values with `--my-variable` syntax and reference them anywhere using `var(--my-variable)`. Unlike preprocessor variables in Sass or Less, they are live in the browser, cascade through the DOM, and can be updated dynamically with JavaScript. They're essential for theming systems, dark mode implementations, and maintaining consistent design tokens across large stylesheets.

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.

Observability is the ability to understand the internal state of a system by examining its external outputs — primarily logs, metrics, and traces (the "three pillars"). Unlike basic monitoring that checks predefined thresholds, observability enables you to ask arbitrary questions about system behavior and debug novel issues. Tools like Grafana, Datadog, and OpenTelemetry provide automated collection and correlation of telemetry data across distributed services.

Blue-green deployment is a release strategy that maintains two identical production environments — "blue" (current) and "green" (new version). Traffic is switched from blue to green only after the new version passes all health checks, enabling zero-downtime releases. If issues are detected, traffic can be instantly routed back to the blue environment, making rollbacks trivial and fully automated.

Focus management is the practice of controlling which element receives keyboard focus in a web application, especially during dynamic content changes. When a modal opens, focus should move into it; when it closes, focus should return to the trigger element. Proper focus management is essential for keyboard and screen reader users, and involves techniques like focus trapping, roving tabindex, and programmatic focus with `element.focus()`.