Then restart the TypeScript server.

Your original import can remain unchanged:

import 'mapbox-gl/dist/mapbox-gl.css'

You don't need to move the CSS file into your own src directory.

Frequently Asked Questions

Why does TypeScript say it cannot find a CSS file that exists?

Because TypeScript needs to resolve the import through its module/type system. The fact that the CSS file exists on disk doesn't automatically provide TypeScript with a module declaration for it.

Adding:

declare module '*.css' {}

tells TypeScript how to treat CSS modules.

Do I need @types/mapbox-gl to fix this error?

Not for the CSS declaration itself.