PostCSS nesting with CSS variables isn't working in Tailwind CSS & Next.js

Question

I am trying to use PostCSS nesting with CSS variables but it doesn't convert CSS variables at all.

Instead it shows Invalid property value in the DOM for CSS Variables.

My tailwind.css file contains a bunch of CSS variables:

tailwind.css

@import 'tailwindcss/base';
@import 'tailwindcss/components';
@import 'tailwindcss/utilities';

@layer base {
  :root {
    --font-mono: 'Fira Mono, monospace';

    --text-1: '12px';
    --text-2: '14px';

    --colors-black: 'rgba(19, 19, 21, 1)';
    --colors-white: 'rgba(255, 255, 255, 1)';
    --colors-gray: 'rgba(128, 128, 128, 1)';
    --colors-blue: 'rgba(3, 136, 252, 1)';
    --colors-red: 'rgba(249, 16, 74, 1)';
    --colors-yellow: 'rgba(255, 221, 0, 1)';
    --colors-pink: 'rgba(232, 141, 163, 1)';
    --colors-turq: 'rgba(0, 245, 196, 1)';
    --colors-orange: 'rgba(255, 135, 31, 1)';

    --space-1: '4px';
    --space-2: '8px';
    --space-3: '16px';

    --radii-1: '2px';
    --radii-2: '4px';
  }

  pre {
    --background: 'hsla(206 12% 89.5% / 5%)';
    --text: var('--colors-white');
    --syntax1: var('--colors-orange');
    --syntax2: var('--colors-turq');
    --syntax3: var('--colors-pink');
    --syntax4: var('--colors-pink');
    --comment: var('--colors-gray');
    --removed: var('--colors-red');
    --added: var('--colors-turq');

    box-sizing: 'border-box';
    padding: var('--space-3');
    overflow: 'auto';
    font-family: var('--font-mono');
    font-size: var('--text-2');
    line-height: var('--space-3');
    whitespace: 'pre';
    background-color: var('--background');
    color: var('--text');

    '& > code': {
      display: 'block';
    }

    '.token.parameter': {
      color: var('--text');
    }

    '.token.tag, .token.class-name, .token.selector, .token.selector .class, .token.function': {
      color: var('--syntax1');
    }

    '.token.attr-value, .token.class, .token.string, .token.number, .token.unit, .token.color': {
      color: var('--syntax2');
    }

    '.token.attr-name, .token.keyword, .token.rule, .token.operator, .token.pseudo-class, .token.important': {
      color: var('--syntax3');
    }

    '.token.punctuation, .token.module, .token.property': {
      color: var('--syntax4');
    }

    '.token.comment': {
      color: var('--comment');
    }

    '.token.atapply .token:not(.rule):not(.important)': {
      color: 'inherit';
    }

    '.language-shell .token:not(.comment)': {
      color: 'inherit';
    }

    '.language-css .token.function': {
      color: 'inherit';
    }

    '.token.deleted:not(.prefix), .token.inserted:not(.prefix)': {
      display: 'block';
      px: '$4';
      mx: '-$4';
    }

    '.token.deleted:not(.prefix)': {
      color: var('--removed');
    }

    '.token.inserted:not(.prefix)': {
      color: var('--added');
    }

    '.token.deleted.prefix, .token.inserted.prefix': {
      userselect: 'none';
    }
  }
}

My PostCSS Config contains postcss-preset-env already which should support for CSS nesting. I also installed postcss-nested & postcss-css-variables, just in case.

postcss.config.js

module.exports = {
  plugins: [
    'postcss-import',
    'tailwindcss',
    'postcss-flexbugs-fixes',
    'postcss-nested',
    'postcss-css-variables',
    [
      'postcss-preset-env',
      {
        autoprefixer: {
          flexbox: 'no-2009',
        },
        stage: 3,
        features: {
          'custom-properties': false,
          'nesting-rules': true,
        },
      },
    ],
  ],
}

Reproduction here → https://github.com/deadcoder0904/postcss-tailwind-next-bug

Run the app & check the DOM to see the CSS variables in the Styles panel which shows Invalid property value.

How can I get CSS variables to work with Tailwind CSS?

Answer 1

The complete solution was to remove quotes & object notation in CSS. I copied the whole thing from CSS-in-JS but forgot to remove quotes & object notation aka :

tailwind.css

@import 'tailwindcss/base';
@import 'tailwindcss/components';
@import 'tailwindcss/utilities';

@layer base {
  :root {
    --font-mono: 'Fira Mono, monospace';

    --text-1: 12px;
    --text-2: 14px;

    --colors-black: rgba(19, 19, 21, 1);
    --colors-white: rgba(255, 255, 255, 1);
    --colors-gray: rgba(128, 128, 128, 1);
    --colors-blue: rgba(3, 136, 252, 1);
    --colors-red: rgba(249, 16, 74, 1);
    --colors-yellow: rgba(255, 221, 0, 1);
    --colors-pink: rgba(232, 141, 163, 1);
    --colors-turq: rgba(0, 245, 196, 1);
    --colors-orange: rgba(255, 135, 31, 1);

    --space-1: 4px;
    --space-2: 8px;
    --space-3: 16px;

    --radii-1: 2px;
    --radii-2: 4px;
  }

  pre {
    --background: hsla(206 12% 89.5% / 5%);
    --text: var(--colors-white);
    --syntax1: var(--colors-orange);
    --syntax2: var(--colors-turq);
    --syntax3: var(--colors-pink);
    --syntax4: var(--colors-pink);
    --comment: var(--colors-gray);
    --removed: var(--colors-red);
    --added: var(--colors-turq);

    box-sizing: border-box;
    padding: var(--space-3);
    overflow: auto;
    font-family: var(--font-mono);
    font-size: var(--text-2);
    line-height: var(--space-3);
    white-space: pre;
    background-color: var(--background);
    color: var(--text);

    & > code {
      display: block;
    }

    .token.parameter {
      color: var(--text);
    }

    .token.tag,
    .token.class-name,
    .token.selector,
    .token.selector .class,
    .token.function {
      color: var(--syntax1);
    }

    .token.attr-value,
    .token.class,
    .token.string,
    .token.number,
    .token.unit,
    .token.color {
      color: var(--syntax2);
    }

    .token.attr-name,
    .token.keyword,
    .token.rule,
    .token.operator,
    .token.pseudo-class,
    .token.important {
      color: var(--syntax3);
    }

    .token.punctuation,
    .token.module,
    .token.property {
      color: var(--syntax4);
    }

    .token.comment {
      color: var(--comment);
    }

    .token.atapply .token:not(.rule):not(.important) {
      color: inherit;
    }

    .language-shell .token:not(.comment) {
      color: inherit;
    }

    .language-css .token.function {
      color: inherit;
    }

    .token.deleted:not(.prefix),
    .token.inserted:not(.prefix) {
      display: block;
      px: $4;
      mx: -$4;
    }

    .token.deleted:not(.prefix) {
      color: var(--removed);
    }

    .token.inserted:not(.prefix) {
      color: var(--added);
    }

    .token.deleted.prefix,
    .token.inserted.prefix {
      userselect: none;
    }
  }
}

And for some reason, in one of my projects, postcss-preset-env didn't work so I had to use postcss-nested & postcss-css-variables in postcss.config.js.

postcss.config.js

module.exports = {
    plugins: [
        'postcss-import',
        'tailwindcss',
        'postcss-flexbugs-fixes',
        'postcss-nested',
        'postcss-custom-properties',
        'autoprefixer',
        // [
        //  'postcss-preset-env',
        //  {
        //      autoprefixer: {
        //          flexbox: 'no-2009',
        //      },
        //      stage: 3,
        //      features: {
        //          'custom-properties': true,
        //          'nesting-rules': true,
        //      },
        //  },
        // ],
    ],
}

But postcss-preset-env worked in another project with the same config. I have tested it multiple times by cleaning cache, reinstalling dependencies & copy-pasted the same config so I'm pretty sure it's not my project's problem.