Modern CSS

HTML and CSS now cover much of the JS work UI libraries did: "popover, anchor, dialog, view transitions, scroll driven animation and custom select" (nerdy.dev: Headless, boneless, skinless & lifeless UI, 2024-10-16, crediting Nils), and models are "barely aware" of it (nerdy.dev: Why AI Sucks At Front End, 2026-04-12). This skill holds that CSS. Every fact comes from Adam Argyle's blog nerdy.dev, tagged with the post and its date, except FONTS-AND-TEXT-DETAILS.md and the few sections tagged with another source ([Craft], [Emil Kowalski, ...], [Jakub Krehel, ...], [corner-smoothing], [css-modern-features], [responsive-craft], [flornkm, ...], [Libraries.dev]), STICKY.md, and the owner's responsive policy and source comparisons in RESPONSIVE.md and RESPONSIVE-FORKS.md, and every feature carries its current status from MDN (Baseline widely, Baseline newly with its date, or Limited availability with the engines), checked October 2026, stated once in the file that introduces it. Where a post's code or support claim has gone stale, the files give the current form and say what the post said; experimental features stay in, marked. Durations, curves, springs (including linear() springs) and staggers for interface motion are in ui-animation SKILL.md; SVG markup, filters and SMIL are in svg SKILL.md; the owner's signed-in app builds its controls, menus and dialogs on headless primitives in app-ui SKILL.md, and where that differs from the native route here, the topic file says so; keeping an interface from looking template-built is anti-slop-ui SKILL.md.

Apply only the routes and checks for the selected job. Read a linked skill's named file from its installed folder when available, or from the linked source. Report an unavailable required reference instead of inventing it. [skill-authoring, DISTRIBUTION.md#composing-skills]