diff --git a/scripts/stylelint-no-specificity-where.mjs b/scripts/stylelint-no-specificity-where.mjs
new file mode 100644
index 00000000..2e2a8492
--- /dev/null
+++ b/scripts/stylelint-no-specificity-where.mjs
@@ -0,0 +1,67 @@
+import stylelint from "stylelint";
+
+const ruleName = "codex-panel/no-specificity-where";
+
+const messages = stylelint.utils.ruleMessages(ruleName, {
+  rejected: (selector) => `Do not hide class, id, or attribute selectors inside :where(): "${selector}"`,
+});
+
+function rule(primary) {
+  return (root, result) => {
+    if (primary === false) return;
+
+    root.walkRules((ruleNode) => {
+      const selector = ruleNode.selector;
+      if (!selector.includes(":where(")) return;
+
+      for (const range of whereRanges(selector)) {
+        const body = selector.slice(range.bodyStart, range.bodyEnd);
+        if (!/[.#[]/.test(body)) continue;
+
+        stylelint.utils.report({
+          message: messages.rejected,
+          messageArgs: [selector.slice(range.start, range.end)],
+          node: ruleNode,
+          result,
+          ruleName,
+          index: range.start,
+          endIndex: range.end,
+        });
+      }
+    });
+  };
+}
+
+function whereRanges(selector) {
+  const ranges = [];
+  let searchFrom = 0;
+
+  while (searchFrom < selector.length) {
+    const start = selector.indexOf(":where(", searchFrom);
+    if (start === -1) break;
+
+    const bodyStart = start + ":where(".length;
+    let depth = 1;
+    let index = bodyStart;
+
+    for (; index < selector.length && depth > 0; index += 1) {
+      const char = selector[index];
+      if (char === "(") depth += 1;
+      if (char === ")") depth -= 1;
+    }
+
+    if (depth === 0) {
+      ranges.push({ start, bodyStart, bodyEnd: index - 1, end: index });
+      searchFrom = index;
+    } else {
+      searchFrom = bodyStart;
+    }
+  }
+
+  return ranges;
+}
+
+rule.ruleName = ruleName;
+rule.messages = messages;
+
+export default stylelint.createPlugin(ruleName, rule);
diff --git a/stylelint.config.mjs b/stylelint.config.mjs
index 6403dcce..3cd8b4d4 100644
--- a/stylelint.config.mjs
+++ b/stylelint.config.mjs
@@ -1,6 +1,15 @@
+import noSpecificityWhere from "./scripts/stylelint-no-specificity-where.mjs";
+
 export default {
   extends: ["stylelint-config-standard"],
+  plugins: [noSpecificityWhere],
   rules: {
+    "codex-panel/no-specificity-where": [
+      true,
+      {
+        severity: "warning",
+      },
+    ],
     "color-named": [
       "never",
       {
diff --git a/styles.css b/styles.css
index 76a0c2ba..fd6d9f57 100644
--- a/styles.css
+++ b/styles.css
@@ -373,7 +373,7 @@
   stroke: currentcolor;
 }
 
-.codex-panel-ui__toolbar-control:not(.is-active):focus:not(:hover):not(:focus-visible) {
+.codex-panel-ui__toolbar-control:where(:focus:not(:hover):not(:focus-visible)) {
   background: transparent;
   box-shadow: none;
   color: var(--icon-color);
@@ -619,24 +619,20 @@
   font-size: var(--codex-panel-toolbar-meta-size);
 }
 
-.codex-panel__toolbar-panel-item:hover:not(:where(:disabled, .is-disabled)) {
+.codex-panel__toolbar-panel-item:hover:not(:disabled):not(.is-disabled) {
   color: var(--nav-item-color-hover, var(--text-normal));
   background: var(--background-modifier-hover);
   box-shadow: none;
   transform: none;
 }
 
-.codex-panel__toolbar-panel-item:hover:not(:where(:disabled, .is-disabled)) .codex-panel__toolbar-panel-label,
-.codex-panel__toolbar-panel-item:focus:not(:where(:disabled, .is-disabled)) .codex-panel__toolbar-panel-label,
-.codex-panel__toolbar-panel-item:focus-visible:not(:where(:disabled, .is-disabled)) .codex-panel__toolbar-panel-label,
-.codex-panel__toolbar-panel-item:active:not(:where(:disabled, .is-disabled)) .codex-panel__toolbar-panel-label {
+.codex-panel__toolbar-panel-item:where(:hover, :focus, :focus-visible, :active):not(:disabled):not(.is-disabled)
+  .codex-panel__toolbar-panel-label {
   color: var(--nav-item-color-hover, var(--text-normal));
 }
 
-.codex-panel__toolbar-panel-item:hover:not(:where(:disabled, .is-disabled)) .codex-panel__toolbar-panel-meta,
-.codex-panel__toolbar-panel-item:focus:not(:where(:disabled, .is-disabled)) .codex-panel__toolbar-panel-meta,
-.codex-panel__toolbar-panel-item:focus-visible:not(:where(:disabled, .is-disabled)) .codex-panel__toolbar-panel-meta,
-.codex-panel__toolbar-panel-item:active:not(:where(:disabled, .is-disabled)) .codex-panel__toolbar-panel-meta {
+.codex-panel__toolbar-panel-item:where(:hover, :focus, :focus-visible, :active):not(:disabled):not(.is-disabled)
+  .codex-panel__toolbar-panel-meta {
   color: var(--nav-item-color-hover, var(--text-normal));
 }
 
@@ -1242,7 +1238,7 @@
   grid-template-columns: minmax(0, 1fr) auto auto;
 }
 
-.codex-panel__thread:hover:not(:where(:disabled, .is-disabled)),
+.codex-panel__thread:hover:not(:disabled):not(.is-disabled),
 .codex-panel__thread.is-checked {
   background: transparent;
 }
@@ -1653,11 +1649,11 @@
   animation: codex-panel-reasoning-dot 1.2s infinite ease-in-out;
 }
 
-.codex-panel__reasoning:where(.is-active) .codex-panel__reasoning-dots span:nth-child(2) {
+.codex-panel__reasoning.is-active .codex-panel__reasoning-dots span:where(:nth-child(2)) {
   animation-delay: 0.18s;
 }
 
-.codex-panel__reasoning:where(.is-active) .codex-panel__reasoning-dots span:nth-child(3) {
+.codex-panel__reasoning.is-active .codex-panel__reasoning-dots span:where(:nth-child(3)) {
   animation-delay: 0.36s;
 }
 
@@ -2093,11 +2089,11 @@
   animation: codex-panel-reasoning-dot 1.2s infinite ease-in-out;
 }
 
-.codex-panel-selection-rewrite__status:where(.is-active) .codex-panel-selection-rewrite__status-dots span:nth-child(2) {
+.codex-panel-selection-rewrite__status.is-active .codex-panel-selection-rewrite__status-dots span:where(:nth-child(2)) {
   animation-delay: 0.18s;
 }
 
-.codex-panel-selection-rewrite__status:where(.is-active) .codex-panel-selection-rewrite__status-dots span:nth-child(3) {
+.codex-panel-selection-rewrite__status.is-active .codex-panel-selection-rewrite__status-dots span:where(:nth-child(3)) {
   animation-delay: 0.36s;
 }
 
diff --git a/tests/styles.test.ts b/tests/styles.test.ts
index 2107483f..318972c8 100644
--- a/tests/styles.test.ts
+++ b/tests/styles.test.ts
@@ -17,14 +17,19 @@ describe("panel CSS token scope", () => {
 });
 
 describe("chat toolbar CSS", () => {
-  it("does not let mouse-focus reset override active toolbar controls", () => {
+  it("keeps mouse-focus reset less specific than active toolbar controls", () => {
     const toolbarMouseFocus =
-      /\.codex-panel-ui__toolbar-control:not\(\.is-active\):focus:not\(:hover\):not\(:focus-visible\) \{(?<body>[^}]+)\}/.exec(styles)
-        ?.groups?.["body"] ?? "";
+      /\.codex-panel-ui__toolbar-control:where\(:focus:not\(:hover\):not\(:focus-visible\)\) \{(?<body>[^}]+)\}/.exec(styles)?.groups?.[
+        "body"
+      ] ?? "";
 
     expect(toolbarMouseFocus).toContain("background: transparent");
     expect(toolbarMouseFocus).toContain("color: var(--icon-color)");
   });
+
+  it("keeps class selectors out of zero-specificity :where selectors", () => {
+    expect(styles).not.toMatch(/:where\([^)]*[.#[]/);
+  });
 });
 
 describe("threads view CSS", () => {