@container queries: Add support for CSS variables/calc inside tailwind config

[adamleithp-mystic]

Love the plug in, but wondering if adding support for CSS variables and or calc() like this:
From my testing on tailwind play this doesn't work:

export default {
  theme: {
    extend: {
      containers: {
        'col-1': 'var(--column-width)',  // or
        'col-2': 'calc(20px*2)',  // or
        'col-3': 'calc(var(--column-width)*3)',
      },
    },
  },
  plugins: [require('@tailwindcss/container-queries')],
}