Tailwind CLI not importing external files

I am using Tailwind CSS 3.0 and have configured it according to the Using with Preprocessors documentation.

My main.css file looks like this:

@import "tailwindcss/base";
@import "./custom-base-styles.css";

@import "tailwindcss/components";
@import "./custom-components.css";

@import "tailwindcss/utilities";

My postcss.config.js looks like this:

module.exports = {
  plugins: {
    "postcss-import": {},
    tailwindcss: {},
    autoprefixer: {}
  }
}

The directory structure looks like this:

Styles/v2
├── custom-base-styles.css
├── custom-components.css
└── main.css
wwwroot/dev
└── v2
    └── main.css

And I execute the following command to build my main.css file:

npx tailwindcss -i ./Styles/v2/main.css -o ./wwwroot/dev/v2/main.css --watch

The build is executed and my wwwroot/dev/v2/main.css file is produced, but none of the additional changes added in my custom styles are included. Also; the --watch argument is listening for changes to the main.css input file, but non of the @import-ed files.