Supported CSS

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Property names and values match the CSS spec exactly — no prefixes, no -unity- renames. Both parsers (tokenizer and rule/property grammar) are hand-rolled for full control over the supported subset and error reporting.

This page covers selectors, the cascade, values/units, and at-rules. The property surface is split across three sub-pages:

CSS Layout — display, box model, flexbox, grid, positioning, overflow/scrolling, logical axes.
CSS Visual — backgrounds, borders, gradients, shadows, opacity, transform, filter, clip-path, masks.
CSS Text — fonts, line-height, alignment, decoration, white-space, wrapping, ellipsis.

For the authoritative supported / partial / parse-only / missing matrix, see CSS_FEATURE_AUDIT.md and CSS_OPEN_GAPS.md at the repo root. This page is a readable overview, not a line-by-line conformance table.

Selectors

Type	Examples
Simple	`*`, `tag`, `.class`, `#id`
Attribute	`[name]`, `[name=val]`, `[name~=val]`, `[name^=val]`, `[name$=val]`, `[name*=val]`
Combinators	descendant (space), child `>`, adjacent `+`, general sibling `~`
Structural pseudo	`:first-child`, `:last-child`, `:only-child`, `:nth-child(an+b)`, `:nth-of-type`, `:empty`, `:not(...)`, `:is(...)`, `:where(...)`, `:has(...)`, `:lang(...)`, `:dir(...)`
State pseudo	`:hover`, `:focus`, `:focus-visible`, `:focus-within`, `:active`, `:link`, `:visited`, `:any-link`, `:target`, `:scope`, `:disabled`, `:enabled`, `:checked`, `:default`, `:required`, `:optional`, `:valid`, `:invalid`, `:user-valid`, `:user-invalid`, `:in-range`, `:out-of-range`, `:read-only`, `:read-write`, `:placeholder-shown`, `:autofill`, `:root`
Pseudo-elements	`::before` / `:before`, `::after` / `:after`, `::placeholder`, `::selection`, `::backdrop`, `::marker`

Specificity follows the spec; !important is honored. State pseudo-classes flip automatically off event-driven interaction state — no controller code.

Known divergence: :nth-child(... of <selector>) parses but the of <selector> filter is dropped — the index counts all children. Use a more specific selector instead.

Cascade & inheritance

Real selector matching, specificity sorting, and source order.
inherit, initial, unset resolve per spec.
revert / revert-layer roll back to the appropriate lower-priority match across origin and layer (up to 4 chained hops; !important inversion is not honored in v1).
var(--name, fallback) with cycle detection; a cycle member refuses its own definition-level fallback (consumer-side fallback still rescues).
Cascade layers (@layer) and nested rules (& > .child).
Shorthand expansion for font, background, border, border-radius, flex, flex-flow, gap, inset, margin/padding, list-style, animation, the logical box/border shorthands, and all.

Values & units

Lengths: px, em, rem, %, vw, vh, vmin, vmax, and the other standard absolute/relative units. 1px = 1 logical pixel; rem/em derive from a 16px base.
Functions: calc(), min(), max(), clamp() — full arithmetic over lengths, percentages, and numbers. attr() (typed forms in the cascade/content path), env() (safe-area names pre-registered; host can register more via EnvironmentVariables.Register).
Colors: #hex, rgb()/rgba(), hsl()/hsla(), named colors, currentColor, color-mix(), light-dark(). Color math runs in linear space.
Container query units (cqw, cqi, …) are not registered — use viewport units or explicit lengths.

At-rules

@import "path.css" — relative and Unity asset paths. The layer(name) / supports(cond) qualifiers parse but the spliced rules are not wrapped/gated (move those into the importing sheet).
@font-face — full descriptor parsing (font-family, src with local()/format(), weight/style/stretch ranges, unicode-range, font-display). Runtime font-matching honors family + first url(); the finer descriptors are parse-only pending a font-selector pipeline.
@media — full feature set: width/height, orientation, aspect-ratio, resolution, prefers-color-scheme, prefers-reduced-motion, hover, pointer, with and/or/not. Evaluated against the UI surface, not the OS window.
@container — container-type: inline-size | size, named and unnamed, width/height/inline-size/block-size/orientation/aspect-ratio features, range form (width >= 320px), style(--prop) queries, nested conditions, and and/or/not. A fresh container-type assignment may take 1–2 frames to settle (the v1 chicken-and-egg: it reads layout-after-previous-cascade size).
@keyframes — see Animations & Transitions.
@supports — reports Weva's actual support.
@scope (CSS Cascade Level 6) — including nested scope chains.
@property — descriptor parsing with inherits / initial-value / syntax; initial-value containing var()/env() is rejected per spec.
@layer — cascade layers.
@namespace — parses but no XML namespace map (prefixed selectors match on the local name).

Known divergences from Chrome

These are intentional or phase-scoped. The full list lives in PLAN.md §11 "Known v1 simplifications".

Default font is Segoe UI, not Arial — intentional. Bare sans-serif resolves to the bundled Segoe-UI-like face (≈1.36× normal line-height) rather than Chrome's Arial (≈1.15×). This is a locked product decision; the resulting uniform y-shifts vs. Chrome are accepted divergence, not bugs. See Text & Fonts.
box-sizing default is content-box (the CSS initial value). Use * { box-sizing: border-box } for the common reset.
line-height: normal resolves taller than Chrome for the same font-size (a consequence of the default-face metrics above).
Layout-specific simplifications (position: sticky single-axis, min-content/max-content treated as auto in flex, etc.) are listed on CSS Layout.
A set of properties parse cleanly but are intentionally inert or reduced — mix-blend-mode non-normal values, animation-composition: add, 3D-transform properties, font-feature-settings, font-variant-numeric, font-size-adjust, font-synthesis-*, container-query units, and others. See AuthoringGuide.md §17 for the full "parses-but-inert" and "partial-support" lists.

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