fix(server): avoid MIME errors for missing CSS

js/loader.js

@@ -239,7 +239,7 @@ const loadFile = (fileName) => {
 					resolve();
 				};
 				stylesheet.onerror = () => {
-					Log.error("Error on loading stylesheet:", fileName);
+					Log.error(`Could not load stylesheet '${fileName}'.`);
 					stylesheet.remove();
 					resolve();
 				};

js/server.js

@@ -164,6 +164,17 @@ class Server {
 				res.status(200).send("OK");
 			});
 
+			// Run after express.static: missing CSS gets a CSS-typed 404 instead of
+			// Express's default HTML 404, which browsers report as a MIME mismatch.
+			const handleMissingStylesheet = (req, res, next) => {
+				if (path.extname(req.path).toLowerCase() !== ".css") {
+					return next();
+				}
+
+				res.status(404).type("text/css").send("");
+			};
+			app.use(handleMissingStylesheet);
+
 			this.#server.on("listening", () => {
 				resolve({
 					app,

tests/e2e/serveronly_spec.js

@@ -34,6 +34,12 @@ describe("App environment", () => {
 		const res = await fetch("http://localhost:8080/nothing");
 		expect(res.status).toBe(404);
 	});
+
+	it("missing stylesheets should return 404 with a CSS content type", async () => {
+		const res = await fetch("http://localhost:8080/config/missing.css");
+		expect(res.status).toBe(404);
+		expect(res.headers.get("content-type")).toMatch(/^text\/css/);
+	});
 });
 
 describe("Check config", () => {