postcss.config.js

module.exports = (ctx) => ({
  map: false,
  plugins: {
    'postcss-import': {},
    'postcss-cssnext': {
      browsers: [
        //
        // Official browser support policy:
        // https://v4-alpha.getbootstrap.com/getting-started/browsers-devices/#supported-browsers
        //
        'Chrome >= 35', // Exact version number here is kinda arbitrary
        // Rather than using Autoprefixer's native "Firefox ESR" version specifier string,
        // we deliberately hardcode the number. This is to avoid unwittingly severely breaking the previous ESR in the event that:
        // (a) we happen to ship a new Bootstrap release soon after the release of a new ESR,
        //     such that folks haven't yet had a reasonable amount of time to upgrade; and
        // (b) the new ESR has unprefixed CSS properties/values whose absence would severely break webpages
        //     (e.g. `box-sizing`, as opposed to `background: linear-gradient(...)`).
        //     Since they've been unprefixed, Autoprefixer will stop prefixing them,
        //     thus causing them to not work in the previous ESR (where the prefixes were required).
        'Firefox >= 38', // Current Firefox Extended Support Release (ESR); https://www.mozilla.org/en-US/firefox/organizations/faq/
        // Note: Edge versions in Autoprefixer & Can I Use refer to the EdgeHTML rendering engine version,
        // NOT the Edge app version shown in Edge's "About" screen.
        // For example, at the time of writing, Edge 20 on an up-to-date system uses EdgeHTML 12.
        // See also https://github.com/Fyrd/caniuse/issues/1928
        'Edge >= 12',
        'Explorer >= 10',
        // Out of leniency, we prefix these 1 version further back than the official policy.
        'iOS >= 8',
        'Safari >= 8',
        // The following remain NOT officially supported, but we're lenient and include their prefixes to avoid severely breaking in them.
        'Android 2.3',
        'Android >= 4',
        'Opera >= 12'
      ]
    },
    'postcss-flexbugs-fixes': {},
    cssnano: {
      autoprefixer: false
    }
  }
})