Can't get custom variant plugin to work

[RedHatter]

I'm trying to create a custom variant but as far as I can tell its not working. I have the following in my postcss config

  tailwind({
    plugins: [
      plugin(function({ addVariant, e }) {
        console.log('plugin')
        addVariant('first-child', ({ modifySelectors, separator }) => {
          console.log('variant')
          modifySelectors(({ className }) => {
            return `.${e(`first-child${separator}${className}`)}:first-child`
          })
        })
      })
    ],
    theme: {
      variants: {
        backgroundColor: ['hover', 'web']
      }
    }
  }),

'plugin' is logged but not 'variant' and no web variant is generated for background-color.