# PostCSS Logical Viewport Units [
][PostCSS]
[
][npm-url] [
][css-url] [
][cli-url] [
][discord]
```bash
npm install @csstools/postcss-logical-viewport-units --save-dev
```
[PostCSS Logical Viewport Units] lets you easily use `vb` and `vi` length units following the [CSS-Values-4 Specification].
```pcss
.foo {
margin: 10vi 20vb;
}
/* becomes */
.foo {
margin: 10vw 20vh;
margin: 10vi 20vb;
}
```
## Usage
Add [PostCSS Logical Viewport Units] to your project:
```bash
npm install postcss @csstools/postcss-logical-viewport-units --save-dev
```
Use it as a [PostCSS] plugin:
```js
const postcss = require('postcss');
const postcssLogicalViewportUnits = require('@csstools/postcss-logical-viewport-units');
postcss([
postcssLogicalViewportUnits(/* pluginOptions */)
]).process(YOUR_CSS /*, processOptions */);
```
[PostCSS Logical Viewport Units] runs in all Node environments, with special
instructions for:
- [Node](INSTALL.md#node)
- [PostCSS CLI](INSTALL.md#postcss-cli)
- [PostCSS Load Config](INSTALL.md#postcss-load-config)
- [Webpack](INSTALL.md#webpack)
- [Next.js](INSTALL.md#nextjs)
- [Gulp](INSTALL.md#gulp)
- [Grunt](INSTALL.md#grunt)
## Options
### inlineDirection
The `inlineDirection` option allows you to specify the direction of the inline axe. The default value is `left-to-right`, which would match any latin language.
**You should tweak this value so that it is specific to your language and writing mode.**
```js
postcssLogicalViewportUnits({
inlineDirection: 'top-to-bottom'
})
```
```pcss
.foo {
margin: 10vi 20vb;
}
/* becomes */
.foo {
margin: 10vh 20vw;
margin: 10vi 20vb;
}
```
Each direction must be one of the following:
- `top-to-bottom`
- `bottom-to-top`
- `left-to-right`
- `right-to-left`
Please do note that transformations won't do anything particular for `right-to-left` or `bottom-to-top`.
### preserve
The `preserve` option determines whether the original notation
is preserved. By default, it is preserved.
```js
postcssLogicalViewportUnits({ preserve: false })
```
```pcss
.foo {
margin: 10vi 20vb;
}
/* becomes */
.foo {
margin: 10vw 20vh;
}
```
[cli-url]: https://github.com/csstools/postcss-plugins/actions/workflows/test.yml?query=workflow/test
[css-url]: https://cssdb.org/#logical-viewport-units
[discord]: https://discord.gg/bUadyRwkJS
[npm-url]: https://www.npmjs.com/package/@csstools/postcss-logical-viewport-units
[PostCSS]: https://github.com/postcss/postcss
[PostCSS Logical Viewport Units]: https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-logical-viewport-units
[CSS-Values-4 Specification]: https://www.w3.org/TR/css-values-4/#viewport-relative-units