how can i define a path for all subdirectories?

My postcss.config.js looks like this:

const themeDir = __dirname + '/../../';

const purgecss = require('@fullhuman/postcss-purgecss')({

    // Specify the paths to all of the template files in your project
    content: [
        themeDir + 'layouts/**/*.html',
        themeDir + 'content/**/*.html',
        'layouts/**/*.html',
        'content/**/*.html',
        // Specify path to own javascript
        themeDir + 'assets/js/**/*.js',
    ],