I'm learning Express and I had a problem with the stylesheet. The console was printing an error related to X-Content-Type-Options: nosniff. After a long search through MDN, I came to an efficient(simple and useful) solution here on Stack Overflow given by Zahid.
You would need to explicitly tell your express app to consider the folder as static to retain the mime type of the file.
Something like:
app.use(express.static("./"));
I hope it helps everyone who is starting out in this world, like me. ✌