PostCSS plugin to unwrap nested rules like how Sass does it.

.phone {
    &_title {
        width: 500px;
        @media (max-width: 500px) {
            width: auto;
        }
        body.is_dark & {
            color: white;
        }
    }
    img {
        display: block;
    }
}

.title {
  font-size: var(--font);

  @at-root html {
      --font: 16px
  }
}

will be processed to:

.phone_title {
    width: 500px;
}
@media (max-width: 500px) {
    .phone_title {
        width: auto;
    }
}
body.is_dark .phone_title {
    color: white;
}
.phone img {
    display: block;
}

.title {
  font-size: var(--font);
}
html {
  --font: 16px
}

Related plugins:

• Use postcss-atroot for @at-root at-rule to move nested child to the CSS root.
• Use postcss-current-selector after this plugin if you want to use current selector in properties or variables values.
• Use postcss-nested-ancestors before this plugin if you want to reference any ancestor element directly in your selectors with ^&.

Alternatives:

• See also postcss-nesting, which implements CSSWG draft (requires the & and introduces @nest).
• postcss-nested-props for nested properties like font-size.

Step 1: Install plugin:

npm install --save-dev postcss postcss-nested

Step 2: Check your project for existing PostCSS config: postcss.config.js in the project root, "postcss" section in package.json or postcss in bundle config.

If you do not use PostCSS, add it according to official docs and set this plugin in settings.

Step 3: Add the plugin to plugins list:

module.exports = {
  plugins: [
+   require('postcss-nested'),
    require('autoprefixer')
  ]
}

By default, plugin will bubble only @media and @supports at-rules. You can add your custom at-rules to this list by bubble option:

postcss([ require('postcss-nested')({ bubble: ['phone'] }) ])

/* input */
a {
  color: white;
  @phone {
    color: black;
  }
}
/* output */
a {
  color: white;
}
@phone {
  a {
    color: black;
  }
}

By default, plugin will unwrap only @font-face, @keyframes and @document at-rules. You can add your custom at-rules to this list by unwrap option:

postcss([ require('postcss-nested')({ unwrap: ['phone'] }) ])

/* input */
a {
  color: white;
  @phone {
    color: black;
  }
}
/* output */
a {
  color: white;
}
@phone {
  color: black;
}

By default, plugin will strip out any empty selector generated by intermediate nesting levels. You can set preserveEmpty to true to preserve them.

.a {
    .b {
        color: black;
    }
}

Will be compiled to:

.a { }
.a .b {
    color: black;
}

This is especially useful if you want to export the empty classes with postcss-modules.