CSS Core Concepts
Eight things worth knowing properly. No basics.
8 topics
Cascade, Specificity & Layers
How the browser picks a winning declaration, and how @layer finally makes that predictable at scale.
core25 minFlexbox & Grid Layout Models
One-dimensional versus two-dimensional layout, the sizing algorithm behind each, and choosing between them without guessing.
core25 minContaining Blocks, Stacking & Formatting Contexts
The invisible boxes that decide where position:fixed anchors, what z-index compares against, and why margins collapse.
deep25 minResponsive Strategy & Container Queries
Moving from viewport breakpoints to component-relative sizing, and the intrinsic techniques that remove media queries entirely.
core25 minDesign Tokens & Theming
Custom properties as a runtime theming layer, the two-tier token model, and switching themes without a flash.
core20 minStyling Architecture Trade-offs
Utility CSS, CSS Modules, CSS-in-JS and vanilla-extract — what each optimises for, and why runtime CSS-in-JS lost ground.
core25 minAnimation & Compositor Performance
Which properties animate cheaply, the modern CSS that replaced JavaScript animation, and respecting reduced motion.
core20 minCSS at Scale
Keeping a stylesheet maintainable across many contributors and years — conventions, dead code, critical CSS, and audits.
deep20 min