border-radius: More Than Just Rounded Corners
The border-radius property rounds an element's corners, used for everything from buttons to circular avatars. The footgun is its shorthand syntax: one value is simple, but two, three, or four values follow specific clockwise rules that are easy to mix up.
CSS `background`: The All-in-One Shorthand
The CSS `background` property is a shortcut for styling an element's backdrop, combining color, image, and position in one line. Use it for most background tasks, from simple colors to complex layered images.
CSS `font`: The All-in-One Typography Shorthand
The `font` property is a single CSS declaration for setting multiple type styles at once, like size, weight, and family. Use it to define base typography for your site or components.
CSS Color Values: From Keywords to Functions
CSS offers multiple ways to define colors, from simple names like `red` to functions like `rgb()`. Use keywords for mockups, hex for design handoffs, and HSL for intuitive manipulation. The main footgun: colors can look different across uncalibrated devices.
CSS Containing Block: The Box That Defines Your Box
An element's size and position are calculated relative to its containing block, not always its direct parent. This determines how percentage widths are resolved and provides the reference for `position: absolute`.
Block Formatting Context: Taming Floats and Margins
A Block Formatting Context (BFC) is a mini-layout sandbox on your page, isolating its contents. Use it to contain child floats that would otherwise overflow their parent, or to stop adjacent elements from collapsing their margins.
CSS Stacking Contexts: The Z-Axis Explained
A CSS stacking context is like a self-contained group of layers. Elements inside only compete for z-index with siblings in that same group. They're created by properties like `position` with `z-index`, `opacity`, or `transform`.
CSS Pseudo-elements: Styling Parts of an Element
Pseudo-elements style parts of an element not in the DOM, like a paragraph's first line or selected text. Use `::before`/`::after` for decorative content or `::selection` to style user highlights.
CSS Margin Collapsing: The Largest Margin Wins
Instead of adding up, vertical margins on adjacent block elements 'collapse' into one, taking the size of the largest margin. This explains why two paragraphs with `margin: 1rem` don't have `2rem` of space between them. The footgun is assuming it's a bug.
CSS Positioning: Taking Elements Out of Normal Flow
CSS `position` lets you override the default document flow. Think of it as telling an element to ignore its neighbors and listen to `top`/`left` coordinates instead. Use it for overlays, modals, and sticky headers.
CSS Pseudo-classes: Style Elements Based on State
CSS pseudo-classes style elements based on their state, not just their HTML structure. Use them for interactive states like `:hover`, form validation like `:invalid`, or structural position like `:first-child`.
CSS box-sizing: Predictable Element Sizing
The `box-sizing` property controls if padding and borders are added outside an element's width or carved out from inside. Using `border-box` makes layouts predictable, ensuring a `width: 100px` box is exactly 100px wide.
CSS 'display': How Elements Occupy Space
The CSS `display` property defines an element's layout role: does it demand its own line (`block`) or share space (`inline`)? It's essential for everything from text flow to complex layouts with `flex` and `grid`.
CSS Inheritance: Styles Flow Downhill
CSS inheritance is like genetics for web elements: children inherit styles like `color` and `font-family` from their parents. This is why setting a font on `<body>` styles a whole page.
CSS Specificity: The Browser's Tie-Breaking Rule
CSS Specificity is the browser's tie-breaking system for conflicting styles. Think of it as a score: an ID is worth more than any number of classes, and a class is worth more than any number of elements. The footgun: using `!important` to win.
Next.js 16 makes the app router the only router
The pages directory is officially deprecated. Migration codemods cover most apps in under an hour, and the new router gets streaming RSC by default.
Server Components, explained without the jargon
RSC is not SSR. This deep-dive walks through the request lifecycle, why client components serialize their props, and where the network boundary actually sits.
React interview cheatsheet: hooks rules in 60 seconds
An interview favourite: list every Rules-of-Hooks violation, then explain why useEffect dependency arrays are not 'reactive' the way useMemo's are.