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# PostCSS Discard Overridden

[PostCSS] plugin to discard overridden `@keyframes` or `@counter-style`.

`@keyframes` or `@counter-style` will be overridden by those who share the same identifiers and appear later in stylesheets. So we can discard all of them except the last one. When defined inside a `@media` or `@supports` rule, `@keyframes` and `@counter-style` rules only override global rules in some of the client browsers so they need handled separately. This plugin has taken care of this and transforms the PostCss AST **safely**.

[PostCSS]: https://github.com/postcss/postcss

```css
@-webkit-keyframes fade-in {
  0% {
    opacity: 0;
  }
  100% {
    opacity: 0.8;
  }
}
@keyframes fade-in {
  0% {
    opacity: 0;
  }
  100% {
    opacity: 0.8;
  }
}
@media (max-width: 500px) {
  @-webkit-keyframes fade-in {
    0% {
      opacity: 0;
    }
    100% {
      opacity: 1;
    }
  }
  @keyframes fade-in {
    0% {
      opacity: 0;
    }
    100% {
      opacity: 1;
    }
  }
  @-webkit-keyframes fade-in {
    0% {
      opacity: 0;
    }
    100% {
      opacity: 0.8;
    }
  }
  @keyframes fade-in {
    0% {
      opacity: 0;
    }
    100% {
      opacity: 0.8;
    }
  }
  @supports (display: flex) {
    @-webkit-keyframes fade-in {
      0% {
        opacity: 0;
      }
      100% {
        opacity: 1;
      }
    }
    @keyframes fade-in {
      0% {
        opacity: 0;
      }
      100% {
        opacity: 1;
      }
    }
  }
}
@-webkit-keyframes fade-in {
  0% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
@keyframes fade-in {
  0% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
```

```css
@media (max-width: 500px) {
  @-webkit-keyframes fade-in {
    0% {
      opacity: 0;
    }
    100% {
      opacity: 0.8;
    }
  }
  @keyframes fade-in {
    0% {
      opacity: 0;
    }
    100% {
      opacity: 0.8;
    }
  }
  @supports (display: flex) {
    @-webkit-keyframes fade-in {
      0% {
        opacity: 0;
      }
      100% {
        opacity: 1;
      }
    }
    @keyframes fade-in {
      0% {
        opacity: 0;
      }
      100% {
        opacity: 1;
      }
    }
  }
}
@-webkit-keyframes fade-in {
  0% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
@keyframes fade-in {
  0% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
```

## Usage

See the [PostCSS documentation](https://github.com/postcss/postcss#usage) for
examples for your environment.

## Contributors

See [CONTRIBUTORS.md](https://github.com/cssnano/cssnano/blob/master/CONTRIBUTORS.md).