Gatsby + TailwindCSS + PostCSS + PurgeCSS

package.json

{
  "name": "example",
  "private": true,
  "description": "A simple starter to get up running with Gatsby + TailwindCSS + PostCSS + PurgeCSS",
  "version": "0.1.0",
  "author": "Lauren Dorman <[email protected]>",
  "dependencies": {
    "gatsby": "^2.19.6",
    "gatsby-image": "^2.2.39",
    "gatsby-plugin-manifest": "^2.2.38",
    "gatsby-plugin-offline": "^2.2.10",
    "gatsby-plugin-postcss": "^2.1.19",
    "gatsby-plugin-react-helmet": "^3.1.21",
    "gatsby-plugin-sharp": "^2.4.2",
    "gatsby-source-filesystem": "^2.1.46",
    "gatsby-transformer-sharp": "^2.3.13",
    "prop-types": "^15.7.2",
    "react": "^16.12.0",
    "react-dom": "^16.12.0",
    "react-helmet": "^5.2.1"
  },
  "devDependencies": {
    "@fullhuman/postcss-purgecss": "^1.3.0",
    "postcss-cli": "^6.1.3",
    "postcss-import": "^12.0.1",
    "postcss-preset-env": "^6.7.0",
    "prettier": "^1.19.1",
    "tailwindcss": "^1.1.4"
  },
  "keywords": [
    "gatsby",
    "tailwindcss",
    "postcss",
    "purgecss"
  ],
  "license": "MIT",
  "scripts": {
    "build": "gatsby build",
    "develop": "gatsby develop",
    "css": "postcss src/styles/index.css -o public/static/css/styles.css",
    "format": "prettier --write \"**/*.{js,jsx,json,md}\"",
    "start": "npm run develop",
    "serve": "gatsby serve",
    "test": "echo \"Write tests! -> https://gatsby.dev/unit-testing \""
  }
}

postcss.config.js

module.exports = () => ({
  plugins: [
    require("postcss-preset-env")({
      stage: 0,
    }),
    require("postcss-import"),
    // See: https://www.gatsbyjs.org/docs/tailwind-css/#option-1-postcss
    require("tailwindcss")("./tailwind.config.js"),
    require("autoprefixer"),
    // See: https://purgecss.com/plugins/postcss.html#usage
    require("@fullhuman/postcss-purgecss")({
      content: ["./src/**/*.js"],
      defaultExtractor: content => content.match(/[\w-/:]+(?<!:)/g) || [],
      whitelist: ['html', 'body', 'gatsby-focus-wrapper']
    }),
    require("cssnano")({
      preset: "default",
    }),
  ],
})