fix(core): inline custom CSS into experience HTML head to prevent style flash#8917
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darcyYe wants to merge 5 commits into
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fix(core): inline custom CSS into experience HTML head to prevent style flash#8917darcyYe wants to merge 5 commits into
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| .changeset/gentle-otters-cheer.md | 📈 +653 Bytes |
| packages/core/src/middleware/koa-experience-ssr.test.ts | 📈 +3.79 KB |
| packages/core/src/middleware/koa-experience-ssr.ts | 📈 +1.92 KB |
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Summary
When custom CSS is configured for the sign-in experience, the hosted page briefly rendered the built-in styles before the custom CSS applied (a flash of built-in content). Custom CSS was only injected client-side via
react-helmet, which mutates<head>asynchronously after the page had already painted.The experience SSR middleware now inlines the tenant's
customCssinto a<style data-custom-css>element in the served HTML<head>, so custom CSS is part of the cascade on the first paint.The pre-existing client-side react-helmet
<style>(inAppMeta.tsx) is intentionally kept and does not reintroduce the flash: the server-inlined<style>already styles the first paint, and the helmet tag — added later with identical CSS — produces no visible repaint. It is kept because it is the only custom-CSS path for live preview: the server deliberately skips inlining in preview mode (?preview=true), where the console iframe pushes styling live viapostMessage. On the real page it re-asserts the same CSS (a harmless duplicate that also acts as a precedence backstop). Removing it would break live preview without improving the fix.customCssinto<head>before the SSR placeholder substitution, so the</head>match only targets the genuine document head.?preview=true), where the console iframe drives styling live viapostMessage+ react-helmet.</style>sequence in custom CSS so it cannot terminate the<style>element early.window.logtoSsrdata through a newserializeSsrDatahelper that escapes</>/&, preventing a</script>in tenant data (custom CSS or custom content) from breaking out of the inline script.This affects the production/self-hosted (and Cloud) build path; in development the experience is proxied to Vite and the middleware is a no-op.
Testing
Unit tests
Checklist
.changeset