postcss.config.js

const css4ColorsToLegacyRgbaPlugin = {
  postcssPlugin: 'these-colors-dont-run',
  Once (root) {
    root.walkDecls((decl) => {
      const rgbRegex = /rgb\((\d{1,3})\s+(\d{1,3})\s+(\d{1,3})\s*(?:\/\s*(\d+\.?\d*))?\)/g
      decl.value = decl.value.replace(rgbRegex, (match, r, g, b, a) => {
        if (!a || a === '1' || a === '1.0') {
          return `rgb(${r}, ${g}, ${b})`
        } else {
          return `rgba(${r}, ${g}, ${b}, ${a})`
        }
      })
    })
  }
}

module.exports = (api) => {
  return {
    plugins: [
      require('postcss-import'),
      require('tailwindcss')({
        config: './config/tailwind.config.mailer.js'
      }),
      require('postcss-css-variables'),
      css4ColorsToLegacyRgbaPlugin
    ]
  }
}