Use when organizing a stylesheet's cascade with `@layer`, scoping component styles with `@scope`, isolating third-party CSS, taming `!important` chains, or replacing descendant-selector trees with low-specificity scoped rules. Prevents the four standard cascade-discipline failures : mixing unlayered and layered author rules (unlayered always wins normal), assuming `!important` follows the same layer order as normal declarations (it is reversed), shipping `@scope` without an `@supports` gate, and using `:scope` where a bare selector was intended (silent class-level specificity bump). Covers `@layer` statement / block / anonymous / nested forms; the unlayered-vs-layered normal-vs-important inversion table; canonical author order (`reset, base, theme, components, utilities`); third-party CSS isolation via `@import ... layer(name)`; `@scope (<root>) to (<limit>)` donut syntax; the `:scope` specificity rule; cascade proximity (smallest DOM hop wins, ordered AFTER specificity and BEFORE source order); Baseline stat
Installer avec Codex ou Claude Copiez ce prompt, collez-le dans Codex, Claude ou un autre assistant, puis laissez-le vérifier la page du skill et l'installer pour vous.
Une commande directe contourne le prompt de vérification. Examinez la source avant de l'exécuter.
Use when organizing a stylesheet's cascade with `@layer`, scoping component styles with `@scope`, isolating third-party CSS, taming `!important` chains, or replacing descendant-selector trees with low-specificity scoped rules. Prevents the four standard cascade-discipline failures : mixing unlayered and layered author rules (unlayered always wins normal), assuming `!important` follows the same layer order as normal declarations (it is reversed), shipping `@scope` without an `@supports` gate, and using `:scope` where a bare selector was intended (silent class-level specificity bump). Covers `@layer` statement / block / anonymous / nested forms; the unlayered-vs-layered normal-vs-important inversion table; canonical author order (`reset, base, theme, components, utilities`); third-party CSS isolation via `@import ... layer(name)`; `@scope (<root>) to (<limit>)` donut syntax; the `:scope` specificity rule; cascade proximity (smallest DOM hop wins, ordered AFTER specificity and BEFORE source order); Baseline status per feature. Keywords: @layer, cascade layers, @scope, :scope, donut scope, layer order, unlayered, !important inversion, important-reversal, proximity cascade, scope proximity, revert-layer, CSSLayerBlockRule, my CSS does not override, !important everywhere, specificity war, layer not winning, third-party CSS overrides my styles, descendant selector too broad, cascade broken, how do I organize CSS, what is @layer, why does !important not work as expected, how to scope styles to a component without classes.
license
MIT
compatibility
Designed for Claude Code. Requires Frontend Design evergreen-2026.
metadata
{"author":"OpenAEC-Foundation","version":"1.0"}
Frontend Syntax : CSS Cascade Layers and Scope
Cascade-discipline reference. Replaces specificity bidding with predictable order via @layer and DOM-proximity-based component scoping via @scope.
Per [[frontend-core-web-standards-baseline]], @scope MUST be gated with @supports at-rule(@scope) or an equivalent feature detection until it reaches Widely Available (around mid-2028).
@layer syntax forms
Form
Example
Purpose
Statement
@layer reset, base, theme, components, utilities;
Declare order
Block
@layer components { .card { ... } }
Add rules to a layer
Anonymous
@layer { p { margin-block: 1rem; } }
One-off implicit layer
Nested
@layer framework { @layer layout { ... } }
Sub-layers
Import
@import "vendor.css" layer(reset);
Import third-party into a layer
The cascade-order inversion table
Declaration kind
Winning layer
Normal author, unlayered vs layered
Unlayered ALWAYS wins
Normal author, layered vs layered
Last-declared layer wins
Important author, unlayered vs layered
Layered ALWAYS wins (reversed)
Important author, layered vs layered
First-declared layer wins (reversed)
This inversion is the single most-misunderstood rule in the cascade. Memorize it. Sources : W3C TR : CSS Cascade 5 §6.4 (verified 2026-05-19), MDN : @layer (verified 2026-05-19).
Canonical author layer order
@layer reset, base, theme, components, utilities;
reset : third-party normalize.css or modern CSS reset.
base : element defaults (html, body, headings, lists, links).
theme : design tokens via custom properties (colors, typography scale).
components : component-scoped rules. ALWAYS use @scope (...) here when DOM-proximity is desired.
ALL author CSS MUST live in one of these layers. NEVER leave declarations unlayered : unlayered always beats layered for normal declarations, which silently breaks the discipline.
@scope syntax forms
Form
Grammar
When
Root only
@scope (<root>) { ... }
Apply from <root> downward, no donut
Root + limit (donut)
@scope (<root>) to (<limit>) { ... }
Stop at <limit> exclusive
Inline
<style>@scope { ... }</style> inside parent
Scope to the containing element
Inline + limit
<style>@scope to (<limit>) { ... }</style>
Inline with donut
Inclusivity overrides : to (<limit> > *) includes <limit> itself in the scope; (<root> > *) excludes <root> itself.
@scope specificity rule
Bare selectors and & inside @scope carry the specificity of the SELECTOR ONLY (the :where(:scope) prefix contributes zero). Explicit :scope adds class-level (0,1,0).
Per W3C TR : CSS Cascade 6 (verified 2026-05-19), proximity is positioned AFTER specificity and BEFORE order of appearance :
1. Origin and Importance
2. Context (encapsulation)
3. Style Attribute
4. Cascade Layers
5. Specificity
6. Scope Proximity <-- new in Level 6
7. Order of Appearance
The rule whose scope root is the FEWEST DOM hops from the matched element wins ties of equal specificity. Rules outside any scope are treated as infinite proximity (lose every tie against scoped rules of equal specificity).
Proximity DOES NOT override !important, cascade layers, or specificity. It only resolves what was previously a source-order tie.
Decision Trees
Decision tree : "Where should this CSS go?"
Third-party reset (normalize.css, modern reset):
-> @import "reset.css" layer(reset);
Element defaults (typography, link colors, body bg):
-> @layer base { html, body, h1, ... { ... } }
Design tokens (custom properties at :root):
-> @layer theme { :root { --color-...: ...; } }
Component rules:
Need predictable order across many components?
-> @layer components { .card { ... } }
Need DOM-proximity (closest ancestor wins)?
-> @layer components { @scope (.card) { ... } }
Both?
-> @layer components { @scope (.card) to (.card .card) { ... } }
Single-purpose utility classes (.visually-hidden, .mt-4):
-> @layer utilities { .visually-hidden { ... } }
ANY author CSS:
NEVER leave unlayered; unlayered beats layered for normal rules.
Decision tree : "@layer or @scope for this isolation?"
Problem : two component-libraries fight over the same class names.
-> @layer (one layer per library). Order = predictable winner.
Problem : descendant selector reaches into a nested component.
Example : .feature .article-body img matches images inside nested cards.
-> @scope (.article-body) to (.card) { img { ... } }
Problem : the SAME component appears nested inside itself, and the outer
version should NOT style the inner instance.
-> @scope (.card) to (.card .card) { ... }
The donut limit stops the cascade at the nested boundary.
Problem : two themes nest in the same DOM (e.g. light inside dark inside light).
-> @scope per theme. Proximity ensures closest theme wins.
Problem : ship a Newly Available feature without a fallback.
-> NEVER. Gate with @supports at-rule(@scope) per
[[frontend-core-web-standards-baseline]].
Decision tree : "Why is my unlayered rule winning over my layered rule?"
Are both rules NORMAL (no !important) ?
-> Yes : unlayered beats layered. By spec.
Fix : move the unlayered rule into a named layer.
NEVER add !important to "fix" this. !important reverses the order
and creates a second bug.
Are both rules IMPORTANT (!important) ?
-> The LAYERED rule wins. Unlayered loses for !important.
This is the second-most-misunderstood inversion.
One normal, one important ?
-> The IMPORTANT rule wins regardless of layering.
Mental Model
Cascade Layers replace the specificity-bidding war with explicit author intent. You declare the layer order once, near the top of your stylesheet, and every later rule resolves through that order without further !important tricks.
The two inversions exist for a deliberate reason. Normal cascade : unlayered rules are usually one-off authoritative declarations the author wrote AFTER seeing a problem; the spec respects that. Important cascade : !important is used most often by USERS overriding AUTHORS (the per-origin reversal of importance), and within author CSS, important rules in deep utility layers should not be trumped by random unlayered overrides; the inversion preserves the intent that important + layered = "I really mean it across the whole project".
@scope is the DOM-aware sibling of @layer. Where @layer orders the cascade by AUTHOR DECLARATION ORDER, @scope orders ties by DOM PROXIMITY. They compose : the inner block of @scope lives inside a @layer, and the cascade walks layer first (criterion 4), then specificity (criterion 5), then proximity (criterion 6).
The bare-selector zero-specificity rule inside @scope is the feature that finally lets authors write img { ... } inside a component without ANY specificity inflation. Compared to the BEM workaround (.card__image) or the :where() wrapper (:where(.card) img), @scope is more local AND more readable.
revert-layer is the inverse operation : roll back to the cascaded value from the previous layer. Useful in utility layers : padding: revert-layer; undoes the component-layer padding and re-exposes the base or theme value.
Patterns
Pattern 1 : Canonical layer order with third-party isolation
A <div class="light"><div class="dark"><div class="light">...</div></div></div> chain now resolves each innermost block against its CLOSEST theme ancestor without any explicit specificity or source-order tricks.
Pattern 4 : revert-layer to undo a component override
