diff --git a/docs/features/publisher.md b/docs/features/publisher.md
index cf4bc0d37..3d65c7130 100644
--- a/docs/features/publisher.md
+++ b/docs/features/publisher.md
@@ -214,9 +214,11 @@ only when its id is used and every known class dependency in its preserved
 selector is used. Ambient
 selector fragments emit when at least one selector-list alternative has all of
 its known class dependencies in use; class-free selectors and supported raw
-blocks stay conservative. The editor canvas calls the same selector and
-memoizes the filtered registry by immutable registry identity + used-id
-signature, so large imported utility catalogs do not become large iframe
+blocks stay conservative. Dependencies follow selector semantics: a class
+inside `:not()` is never one, and the alternatives of `:is()`/`:where()` are
+each sufficient rather than all required. The editor canvas calls the same
+selector and memoizes the filtered registry by immutable registry identity +
+used-id signature, so large imported utility catalogs do not become large iframe
 stylesheets. A full precompiled Tailwind catalog can therefore remain
 picker-addressable while the `style` bundle contains only selected utilities
 plus global preflight.
diff --git a/src/__tests__/publisher/styleRuleTreeShake.test.ts b/src/__tests__/publisher/styleRuleTreeShake.test.ts
new file mode 100644
index 000000000..a203534c7
--- /dev/null
+++ b/src/__tests__/publisher/styleRuleTreeShake.test.ts
@@ -0,0 +1,115 @@
+import { describe, it, expect } from 'bun:test'
+import { treeShakeStyleRules } from '@core/publisher'
+import type { StyleRule } from '@core/page-tree'
+
+const cls = (id: string, name: string): StyleRule =>
+  ({
+    id,
+    name,
+    kind: 'class',
+    selector: `.${name}`,
+    styles: {},
+    contextStyles: {},
+    order: 0,
+    createdAt: 0,
+    updatedAt: 0,
+  }) as unknown as StyleRule
+
+const ambient = (id: string, selector: string): StyleRule =>
+  ({
+    id,
+    name: selector,
+    kind: 'ambient',
+    selector,
+    styles: { float: 'left' },
+    contextStyles: {},
+    order: 0,
+    createdAt: 0,
+    updatedAt: 0,
+  }) as unknown as StyleRule
+
+// Known and used: header, nav, p1. Known but unused: cart-button, p2, gone.
+const rules: Record<string, StyleRule> = {
+  header: cls('header', 'header'),
+  nav: cls('nav', 'nav'),
+  cart: cls('cart', 'cart-button'),
+  p1: cls('p1', 'p1'),
+  p2: cls('p2', 'p2'),
+  gone: cls('gone', 'gone'),
+  padding: ambient('padding', '.header .nav > li > a:not(.cart-button)'),
+  notList: ambient('notList', '.nav a:not(.gone, .cart-button)'),
+  notCompound: ambient('notCompound', '.nav a:not(.gone.p2)'),
+  notComplex: ambient('notComplex', '.nav a:not(.gone .p2)'),
+  nestedNot: ambient('nestedNot', '.nav:not(:is(.gone, .p2)) a'),
+  where: ambient('where', '.header:where(.p1, .p2) .nav'),
+  whereDead: ambient('whereDead', '.header:where(.gone, .p2) .nav'),
+  is: ambient('is', ':is(.gone, .nav) a'),
+  isComplexAlt: ambient('isComplexAlt', ':is(.gone .p1, .header .p1) a'),
+  isAllComplexDead: ambient('isAllComplexDead', ':is(.gone .p1, .header .p2) a'),
+  isNotInside: ambient('isNotInside', ':is(.nav:not(.gone), .p2) a'),
+  isThenDeadOutside: ambient('isThenDeadOutside', ':is(.p1, .nav) .gone'),
+  has: ambient('has', '.header:has(.gone)'),
+  hasNot: ambient('hasNot', '.header:has(a:not(.gone))'),
+  nthOf: ambient('nthOf', '.nav > :nth-child(2n of .gone)'),
+  pseudoEl: ambient('pseudoEl', '.nav a:not(.gone)::after'),
+  upper: ambient('upper', '.nav a:NOT(.gone)'),
+  webkitAny: ambient('webkitAny', ':-webkit-any(.gone, .nav) a'),
+  escaped: ambient('escaped', '.hover\\:not-gone:hover .nav'),
+  attr: ambient('attr', '.nav a[title=":not(.gone)"]'),
+  unbalanced: ambient('unbalanced', '.nav a:not(.gone'),
+  bracketParen: ambient('bracketParen', '.nav a:not([x) .gone] .p1'),
+  emptyIs: ambient('emptyIs', '.nav:is() a'),
+  unknownStillKept: ambient('unknownStillKept', '.nav .not-in-registry'),
+  plainDead: ambient('plainDead', '.nav .gone'),
+}
+const used = new Set(['header', 'nav', 'p1'])
+const shaken = treeShakeStyleRules(rules, used)
+const kept = (id: string) => shaken[id] !== undefined
+
+describe('treeShakeStyleRules — negation and alternation semantics', () => {
+  it('does not treat a negated class as a dependency', () => {
+    expect(kept('padding')).toBe(true)
+    expect(kept('notList')).toBe(true)
+    expect(kept('notCompound')).toBe(true)
+    expect(kept('notComplex')).toBe(true)
+    expect(kept('nestedNot')).toBe(true)
+    expect(kept('pseudoEl')).toBe(true)
+    expect(kept('upper')).toBe(true)
+    expect(kept('hasNot')).toBe(true)
+  })
+
+  it('treats :is()/:where() arguments as alternatives, not a conjunction', () => {
+    expect(kept('where')).toBe(true)
+    expect(kept('is')).toBe(true)
+    expect(kept('isComplexAlt')).toBe(true)
+    expect(kept('isNotInside')).toBe(true)
+    expect(kept('webkitAny')).toBe(true)
+  })
+
+  it('still drops a rule whose every alternative depends on an unused class', () => {
+    expect(kept('whereDead')).toBe(false)
+    expect(kept('isAllComplexDead')).toBe(false)
+  })
+
+  it('still requires classes outside the alternation', () => {
+    expect(kept('isThenDeadOutside')).toBe(false)
+    expect(kept('plainDead')).toBe(false)
+  })
+
+  it('still treats :has() and nth-child(of) arguments as required', () => {
+    expect(kept('has')).toBe(false)
+    expect(kept('nthOf')).toBe(false)
+  })
+
+  it('ignores pseudo-shaped text inside escapes and attribute strings', () => {
+    expect(kept('escaped')).toBe(true)
+    expect(kept('attr')).toBe(true)
+  })
+
+  it('keeps malformed and empty pseudos (conservative)', () => {
+    expect(kept('unbalanced')).toBe(true)
+    expect(kept('bracketParen')).toBe(true)
+    expect(kept('emptyIs')).toBe(true)
+    expect(kept('unknownStillKept')).toBe(true)
+  })
+})
diff --git a/src/core/publisher/styleRuleTreeShake.ts b/src/core/publisher/styleRuleTreeShake.ts
index 854b15e79..54a8b2718 100644
--- a/src/core/publisher/styleRuleTreeShake.ts
+++ b/src/core/publisher/styleRuleTreeShake.ts
@@ -88,16 +88,150 @@ export function usedStyleRuleIdSignature(
   return [...collectUsedStyleRuleIds(site)].sort().join('\0')
 }
 
+const NEGATION_PSEUDOS: ReadonlySet<string> = new Set(['not'])
+const ALTERNATION_PSEUDOS: ReadonlySet<string> = new Set([
+  'is',
+  'where',
+  'matches',
+  '-webkit-any',
+  '-moz-any',
+])
+
+interface SelectorPartShape {
+  /**
+   * The selector text outside negation and alternation pseudos. Every class
+   * token here must be present for the part to match (conjunction), which also
+   * covers `:has(.x)` and `:nth-child(n of .x)`: their arguments are kept in
+   * place because they demand the class just like a plain compound does.
+   */
+  conjunctive: string
+  /** One entry per `:is()`/`:where()` group: the part matches only if SOME alternative can. */
+  alternations: string[][]
+}
+
+function readFunctionalPseudoName(selector: string, colonIndex: number): string | null {
+  let index = colonIndex + 1
+  if (selector[index] === ':') return null
+  let name = ''
+  while (index < selector.length && /[\w-]/.test(selector[index])) {
+    name += selector[index]
+    index += 1
+  }
+  if (!name || selector[index] !== '(') return null
+  return name.toLowerCase()
+}
+
+function findClosingParen(selector: string, openIndex: number): number {
+  let depth = 0
+  let bracketDepth = 0
+  let quote: '"' | "'" | null = null
+  for (let index = openIndex; index < selector.length; index += 1) {
+    const char = selector[index]
+    if (quote) {
+      if (char === '\\') index += 1
+      else if (char === quote) quote = null
+      continue
+    }
+    if (char === '"' || char === "'") quote = char
+    else if (char === '\\') index += 1
+    else if (char === '[') bracketDepth += 1
+    else if (char === ']') bracketDepth = Math.max(0, bracketDepth - 1)
+    else if (bracketDepth > 0) continue
+    else if (char === '(') depth += 1
+    else if (char === ')') {
+      depth -= 1
+      if (depth === 0) return index
+    }
+  }
+  return selector.length - 1
+}
+
+/**
+ * Split one selector-list part into the text whose classes are all required
+ * and the `:is()`/`:where()` groups whose alternatives are each sufficient.
+ *
+ * `:not(...)` is removed outright. A negated class is not a dependency: the
+ * selector matches MORE elements when that class is absent, so a class no node
+ * carries can never be grounds for dropping the rule. The shape that forced
+ * this is a theme padding every nav link with `.nav > li > a:not(.cart-button)`:
+ * nothing on the site carries `.cart-button`, the rule was dropped, and every
+ * nav link lost its padding.
+ *
+ * `extractCssSelectorClasses` reports each token's `functionalDepth`, but depth
+ * alone cannot tell `:not(.x)` (never required) from `:has(.x)` or
+ * `:nth-child(n of .x)` (required), so the pseudo name has to be read here.
+ */
+function splitSelectorPartShape(part: string): SelectorPartShape {
+  let conjunctive = ''
+  const alternations: string[][] = []
+  let quote: '"' | "'" | null = null
+  let attributeDepth = 0
+
+  for (let index = 0; index < part.length; index += 1) {
+    const char = part[index]
+    if (quote) {
+      conjunctive += char
+      if (char === '\\' && index + 1 < part.length) {
+        index += 1
+        conjunctive += part[index]
+      } else if (char === quote) quote = null
+      continue
+    }
+    if (char === '"' || char === "'") {
+      quote = char
+      conjunctive += char
+      continue
+    }
+    if (char === '\\') {
+      conjunctive += char
+      if (index + 1 < part.length) {
+        index += 1
+        conjunctive += part[index]
+      }
+      continue
+    }
+    if (char === '[') attributeDepth += 1
+    else if (char === ']') attributeDepth = Math.max(0, attributeDepth - 1)
+    if (char === ':' && attributeDepth === 0) {
+      const name = readFunctionalPseudoName(part, index)
+      if (name && (NEGATION_PSEUDOS.has(name) || ALTERNATION_PSEUDOS.has(name))) {
+        const openIndex = index + 1 + name.length
+        const closeIndex = findClosingParen(part, openIndex)
+        if (ALTERNATION_PSEUDOS.has(name)) {
+          const inner = part.slice(openIndex + 1, closeIndex)
+          const alternatives = splitCssSelectorList(inner)
+          if (alternatives.length > 0) alternations.push(alternatives)
+        }
+        index = closeIndex
+        continue
+      }
+    }
+    conjunctive += char
+  }
+
+  return { conjunctive, alternations }
+}
+
 function selectorPartCanMatch(
   selector: string,
   knownClassNames: ReadonlySet<string>,
   usedClassNames: ReadonlySet<string>,
 ): boolean {
-  for (const token of extractCssSelectorClasses(selector)) {
+  const { conjunctive, alternations } = splitSelectorPartShape(selector)
+  for (const token of extractCssSelectorClasses(conjunctive)) {
     if (knownClassNames.has(token.name) && !usedClassNames.has(token.name)) {
       return false
     }
   }
+  for (const alternatives of alternations) {
+    if (
+      !alternatives.some((alternative) =>
+        selectorPartCanMatch(alternative, knownClassNames, usedClassNames),
+      )
+    ) {
+      return false
+    }
+  }
   return true
 }
 
@@ -119,6 +253,10 @@ function selectorCanMatch(
  * in at least one selector-list alternative. Class-free selectors and raw
  * stylesheet blocks stay conservative because their reach cannot be inferred
  * from node class ids alone.
+ *
+ * "Dependency" follows selector semantics: a class inside `:not()` is never
+ * one (the rule matches more when it is absent), and the alternatives of
+ * `:is()`/`:where()` are each sufficient rather than all required.
  */
 export function treeShakeStyleRules(
   styleRules: Record<string, StyleRule>,