Next.js production build doesn’t apply css variables

I have the next postcss config

module.exports = {
  plugins: [
    [
      'postcss-preset-env',
      {
        browsers: 'last 2 versions, IE 11, not dead',
        preserve: false,
        features: {
          'custom-media-queries': true,
          'custom-properties': true,
          'nesting-rules': true
        },
        importFrom: ['src/styles/variables.css']
      }
    ]
  ]
}

And this file with css variables

@custom-media --desktop screen and (min-width: 768px);
@custom-media --mobile screen and (max-width: 767px);

:root {
  ...some colors
}

After i built my project via next build && next export, colors are not displayed correctly. For example, color: var(–green), instead color: green. Has anybody idea what’s wrong?