site/tailwind.config.js

const defaultTheme = require('tailwindcss/defaultTheme')

module.exports = {
  content: [
    './src/css/**/*',
    './src/pages/**/*'
  ],
  theme: {
    extend: {
      fontFamily: {
        sans: ['"Open Sans"', ...defaultTheme.fontFamily.sans]
      }
    }
  },
  plugins: []
}