Neat idea. I tried it on my site (https://anderegg.ca/) which already inlines its CSS, and got an error from the underlying library (https://www.npmjs.com/package/penthouse):
{"error":true,"name":"Error","message":"css should not be empty","stack":"Error: css should not be empty\n at module.exports (/usr/src/app/node_modules/penthouse/lib/index.js:206:14)\n at file:///usr/src/app/server.js:153:31\n at process.processTicksAndRejections (node:internal/process/task_queues:95:5)"} replies(1):