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# CSS Blank Pseudo [<img src="http://jonathantneal.github.io/js-logo.svg" alt="" width="90" height="90" align="right">][CSS Blank Pseudo]
[![NPM Version][npm-img]][npm-url]
[![Build Status][cli-img]][cli-url]
[![Support Chat][git-img]][git-url]
[CSS Blank Pseudo] lets you style form elements when they are empty, following
the [Selectors Level 4] specification.
```css
input {
/* style an input */
}
input:blank {
/* style an input without a value */
}
```
## Usage
From the command line, transform CSS files that use `:blank` selectors:
```bash
npx css-blank-pseudo SOURCE.css TRANSFORMED.css
```
Next, use your transformed CSS with this script:
```html
<link rel="stylesheet" href="TRANSFORMED.css">
<script src="https://unpkg.com/css-blank-pseudo/browser"></script>
<script>cssBlankPseudo(document)</script>
```
That’s it. The script is 509 bytes and works in all browsers.
---
If you support Internet Explorer 11, use the **browser legacy** script, which
is 671 bytes:
```html
<link rel="stylesheet" href="TRANSFORMED.css">
<script src="https://unpkg.com/css-blank-pseudo/browser-legacy"></script>
<script>cssBlankPseudo(document)</script>
```
## How it works
The [PostCSS plugin](README-POSTCSS.md) clones rules containing `:blank`,
replacing them with an alternative `[blank]` selector.
```css
input:blank {
background-color: yellow;
}
/* becomes */
input[blank] {
background-color: yellow;
}
input:blank {
background-color: yellow;
}
```
Next, the [JavaScript library](README-BROWSER.md) adds a `blank` attribute to
elements otherwise matching `:blank` natively.
```html
<input value="" blank>
<input value="This element has a value">
```
[cli-img]: https://img.shields.io/travis/csstools/css-blank-pseudo/master.svg
[cli-url]: https://travis-ci.org/csstools/css-blank-pseudo
[git-img]: https://img.shields.io/badge/support-chat-blue.svg
[git-url]: https://gitter.im/postcss/postcss
[npm-img]: https://img.shields.io/npm/v/css-blank-pseudo.svg
[npm-url]: https://www.npmjs.com/package/css-blank-pseudo
[CSS Blank Pseudo]: https://github.com/csstools/css-blank-pseudo
[PostCSS Preset Env]: https://preset-env.cssdb.org/
[Selectors Level 4]: https://drafts.csswg.org/selectors-4/#blank