Simplify PostCSS config

Removes workarounds previously needed for the webpack example

postcss.config.mjs

@@ -1,5 +1,3 @@
-import { parse } from 'path'
-
 import autoprefixer from 'autoprefixer'
 import cssnano from 'cssnano'
 import cssnanoPresetDefault from 'cssnano-preset-default'
@@ -20,25 +18,20 @@ import { isDev } from './tasks/task-arguments.mjs'
  * @param {import('postcss-load-config').ConfigContext} ctx - PostCSS context
  * @returns {import('postcss-load-config').Config} PostCSS config
  */
-export default function postcssConfig (ctx) {
+export default ({ from = '', to = '', env = 'production' }) => {
   const plugins = []
-  const syntax = ctx.to?.endsWith('.scss') ? scss : postcss
-
-  // PostCSS 'from' (or webpack 'file') source path
-  // https://github.com/postcss/postcss-load-config#options
-  const { dir, name } = parse(ctx.from || ctx.file || '')
 
-  // IE8 stylesheets
-  const isIE8 = name?.endsWith('-ie8') || name?.endsWith('-ie8.min')
+  // Browserslist IE8 environment
+  if (from.includes('-ie8')) {
+    env = 'oldie'
+  }
 
   // Add vendor prefixes
-  plugins.push(autoprefixer({
-    env: isIE8 ? 'oldie' : ctx.env
-  }))
+  plugins.push(autoprefixer({ env }))
 
   // Add review app auto-generated 'companion' classes for each pseudo-class
   // For example ':hover' and ':focus' classes to simulate form label states
-  if (minimatch(dir, '**/app/stylesheets')) {
+  if (minimatch(from, '**/app/stylesheets/*')) {
     plugins.push(pseudoclasses({
       allCombinations: true,
       restrictTo: [
@@ -52,7 +45,7 @@ export default function postcssConfig (ctx) {
   }
 
   // Transpile CSS for Internet Explorer
-  if (isIE8) {
+  if (env === 'oldie') {
     plugins.push(
       unmq(),
       unopacity({ browsers: 'ie 8' }),
@@ -72,6 +65,9 @@ export default function postcssConfig (ctx) {
     })
   }
 
+  // Sass syntax support
+  const syntax = to.endsWith('.scss') ? scss : postcss
+
   // Always minify CSS
   if (syntax !== scss) {
     plugins.push(cssnano({