feat: add Link HTTP headers for CSS bundle

.github/workflows/build.yml

@@ -22,3 +22,12 @@ jobs:
       - run: npm install
       - name: Test Build
         run: npm run build
+      - name: Commit updated vercel.json
+        if: github.event_name == 'pull_request'
+        run: |
+          git diff --quiet vercel.json && exit 0
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git add vercel.json
+          git commit -m "chore: update CSS preload headers in vercel.json"
+          git push origin HEAD:${{ github.head_ref }}

docusaurus.config.ts

@@ -151,6 +151,7 @@ const config: Config = {
     //     buttonPosition: "center-right",
     //   },
     // ],
+    "./src/plugins/preload-css",
     async function tailwindcss(context, options) {
       return {
         name: "docusaurus-tailwindcss",

src/plugins/preload-css.js

@@ -0,0 +1,54 @@
+// Copyright © 2026 Ory Corp
+// SPDX-License-Identifier: Apache-2.0
+
+const fs = require("fs")
+const path = require("path")
+
+module.exports = function preloadCssPlugin() {
+  return {
+    name: "preload-css",
+    async postBuild({ outDir, siteConfig }) {
+      const cssDir = path.join(outDir, "assets", "css")
+      if (!fs.existsSync(cssDir)) return
+
+      const cssFiles = fs.readdirSync(cssDir).filter((f) => f.endsWith(".css"))
+      if (cssFiles.length === 0) return
+
+      const baseUrl = siteConfig.baseUrl.replace(/\/$/, "")
+      const linkValue = cssFiles
+        .map((f) => `<${baseUrl}/assets/css/${f}>; rel=preload; as=style`)
+        .join(", ")
+
+      const vercelJsonPath = path.join(__dirname, "..", "..", "vercel.json")
+      const vercelJson = JSON.parse(fs.readFileSync(vercelJsonPath, "utf-8"))
+
+      // Remove any existing preload header entries we previously added
+      vercelJson.headers = vercelJson.headers.filter(
+        (h) =>
+          h.source !== "/docs/:path*" ||
+          !h.headers.some((hh) => hh.key === "Link"),
+      )
+
+      // Add Link preload header for all doc pages
+      vercelJson.headers.push({
+        source: "/docs/:path*",
+        headers: [
+          {
+            key: "Link",
+            value: linkValue,
+          },
+        ],
+      })
+
+      fs.writeFileSync(
+        vercelJsonPath,
+        JSON.stringify(vercelJson, null, 2) + "\n",
+      )
+
+      console.log(
+        "[preload-css] Updated vercel.json with %d CSS preload links",
+        cssFiles.length,
+      )
+    },
+  }
+}