Tw, @Tw/cli, etc: 4.1.16
Rollup 4.52.5
Node: 22.21.1, npm/npx: 10.9.4
OS: Windows 11

[6.33 sec] > npm start > accutheme-tw4@2025.10.21 start > npx @tailwindcss/cli -i ./src/tailwind/index.css -o ./dist/theme.css --watch ≈ tailwindcss v4.1.16 Error: Invalid declaration: `*/` 

I hope you will agree this should report the path/filename and line number.

It was simply this line in a .css file, but with zero details it took a while poking around to find.
/* margin-bottom: calc(var(--spacing) * 5); */ */