From 63b4c3652dfe0d4b692dd9278b5f668a0b67a76b Mon Sep 17 00:00:00 2001
From: sliang-code <sihanlia@andrew.cmu.edu>
Date: Sat, 22 Aug 2026 04:59:35 +0800
Subject: [PATCH] fix: don't apply scoped CSS class to elements inside
 <svelte:head> (#18160)

skip elements inside head, they should not get hashes

---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>
---
 .changeset/hungry-plums-roll.md                       |  5 +++++
 .../src/compiler/phases/2-analyze/css/css-prune.js    | 10 ++++++++++
 .../samples/head-css-no-class/_expected_head.html     |  1 +
 .../hydration/samples/head-css-no-class/main.svelte   | 11 +++++++++++
 4 files changed, 27 insertions(+)
 create mode 100644 .changeset/hungry-plums-roll.md
 create mode 100644 packages/svelte/tests/hydration/samples/head-css-no-class/_expected_head.html
 create mode 100644 packages/svelte/tests/hydration/samples/head-css-no-class/main.svelte

diff --git a/.changeset/hungry-plums-roll.md b/.changeset/hungry-plums-roll.md
new file mode 100644
index 0000000000..b5e3688eb5
--- /dev/null
+++ b/.changeset/hungry-plums-roll.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: never apply class hash to elements inside `<svelte:head>`
diff --git a/packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js b/packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js
index 39f485a9f7..dff6bb9b5a 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js
@@ -122,6 +122,13 @@ const any_selector = {
  */
 const seen = new Set();
 
+/**
+ * @param {Compiler.AST.RegularElement | Compiler.AST.SvelteElement | Compiler.AST.RenderTag | Compiler.AST.Component | Compiler.AST.SvelteComponent | Compiler.AST.SvelteSelf} node
+ */
+function is_inside_svelte_head(node) {
+	return node.metadata.path.some((ancestor) => ancestor.type === 'SvelteHead');
+}
+
 /**
  *
  * @param {Compiler.AST.CSS.StyleSheet} stylesheet
@@ -143,6 +150,9 @@ export function prune(stylesheet, elements) {
 				seen.clear();
 
 				if (
+					// Elements rendered through <svelte:head> are not style-scopable.
+					// Prevent css hash injection (class="s-...") on tags like <meta>, <link>, <script>.
+					!is_inside_svelte_head(element) &&
 					apply_selector(
 						selectors,
 						/** @type {Compiler.AST.CSS.Rule} */ (node.metadata.rule),
diff --git a/packages/svelte/tests/hydration/samples/head-css-no-class/_expected_head.html b/packages/svelte/tests/hydration/samples/head-css-no-class/_expected_head.html
new file mode 100644
index 0000000000..497ca987cc
--- /dev/null
+++ b/packages/svelte/tests/hydration/samples/head-css-no-class/_expected_head.html
@@ -0,0 +1 @@
+<meta name="author" content="Re:Designed"> <link rel="author" href="https://example.com"> <script type="application/ld+json"></script>
\ No newline at end of file
diff --git a/packages/svelte/tests/hydration/samples/head-css-no-class/main.svelte b/packages/svelte/tests/hydration/samples/head-css-no-class/main.svelte
new file mode 100644
index 0000000000..29336a17ba
--- /dev/null
+++ b/packages/svelte/tests/hydration/samples/head-css-no-class/main.svelte
@@ -0,0 +1,11 @@
+<svelte:head>
+	<meta name="author" content="Re:Designed" />
+	<link rel="author" href="https://example.com" />
+	<script type="application/ld+json"></script>
+</svelte:head>
+
+<div>dummy</div>
+
+<style>
+	* { color: red }
+</style>