stylis-pxtorem/README.md

A CSS post-processor that converts px to rem.

# stylis-pxtorem [![NPM version](https://badge.fury.io/js/stylis-pxtorem.svg)](http://badge.fury.io/js/stylis-pxtorem)

A plugin for [Stylis](https://stylis.js.org/) that generates rem units from pixel units. 

This is a port of the fantastic [postcss-pxtorem](https://github.com/cuth/postcss-pxtorem) by [cuth](https://github.com/cuth/) to stylis.

## Install

```shell
$ yarn add --dev stylis-pxtorem 
```

## Usage

Pixels are the easiest unit to use (*opinion*). The only issue with them is that they don't let browsers change the default font size of 16. This script converts every px value to a rem from the properties you choose to allow the browser to set the font size.


### Input/Output

*With the default settings, only font related properties are targeted.*

```css
// input
h1 {
    margin: 0 0 20px;
    font-size: 32px;
    line-height: 1.2;
    letter-spacing: 1px;
}

// output
h1 {
    margin: 0 0 20px;
    font-size: 2rem;
    line-height: 1.2;
    letter-spacing: 0.0625rem;
}
```

### options

Type: `Object | Null`  
Default:
```js
{
    rootValue: 16,
    unitPrecision: 5,
    propList: ['font', 'font-size', 'line-height', 'letter-spacing'],
    selectorBlackList: [],
    replace: true,
    mediaQuery: false,
    minPixelValue: 0
}
```

- `rootValue` (Number) The root element font size.
- `unitPrecision` (Number) The decimal numbers to allow the REM units to grow to.
- `propList` (Array) The properties that can change from px to rem.
    - Values need to be exact matches.
    - Use wildcard `*` to enable all properties. Example: `['*']`
    - Use `*` at the start or end of a word. (`['*position*']` will match `background-position-y`)
    - Use `!` to not match a property. Example: `['*', '!letter-spacing']`
    - Combine the "not" prefix with the other prefixes. Example: `['*', '!font*']` 
- `selectorBlackList` (Array) The selectors to ignore and leave as px.
    - If value is string, it checks to see if selector contains the string.
        - `['body']` will match `.body-class`
    - If value is regexp, it checks to see if the selector matches the regexp.
        - `[/^body$/]` will match `body` but not `.body`
- `replace` (Boolean) replaces rules containing rems instead of adding fallbacks.
- `mediaQuery` (Boolean) Allow px to be converted in media queries.
- `minPixelValue` (Number) Set the minimum pixel value to replace.

### A message about ignoring properties
Currently, the easiest way to have a single property ignored is to use a capital in the pixel unit declaration.

```css
// `px` is converted to `rem`
.convert {
    font-size: 16px; // converted to 1rem
}

// `Px` or `PX` is ignored by `postcss-pxtorem` but still accepted by browsers
.ignore {
    border: 1Px solid; // ignored
    border-width: 2PX; // ignored
}
```