Reconciliation

Flexbox (Flexible Box Layout) is a one-dimensional CSS layout model designed for distributing space and aligning items within a container along a single axis — either horizontal or vertical. It excels at handling dynamic content sizes, centering elements, and creating flexible navigation bars, card rows, and form layouts. Properties like `justify-content`, `align-items`, and `flex-grow` give you fine-grained control over how items share available space.

Container Queries allow CSS styles to respond to the size of a parent container rather than the browser viewport, solving a long-standing limitation of media queries. By marking an element as a containment context with `container-type`, its children can use `@container` rules to adapt their layout based on the container's dimensions. This makes truly reusable components possible — a card component can rearrange itself whether it's in a sidebar or a full-width section.

Optimistic UI is a pattern where the interface immediately reflects the expected result of a user action before the server confirms it. For example, a "like" button instantly shows the liked state while the API request happens in the background. This makes the app feel significantly faster and more responsive. If the server request fails, the UI rolls back to the previous state and notifies the user.

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.

CSS-in-JS is an approach where styles are written directly in JavaScript files, often co-located with the components they style. Libraries like Styled Components, Emotion, and Stitches generate unique class names at build time or runtime, eliminating style conflicts. While it enables dynamic styling based on props and full encapsulation, the trend has shifted toward zero-runtime solutions and utility-first CSS due to performance concerns.

Media queries are a CSS feature that allows you to apply styles conditionally based on device characteristics like viewport width, height, orientation, color scheme preference, or reduced motion settings. They are the backbone of responsive web design, enabling different layouts for mobile, tablet, and desktop screens. Modern media queries also support user preference detection with `prefers-color-scheme` and `prefers-reduced-motion` for more accessible experiences.