Bootstrap utilities are generated with our utility API and can be used to modify or extend our default set of utility classes via Sass. Our utility API is based on a series of Sass maps and functions for generating families of classes with various options. If you're unfamiliar with Sass maps, read up on the [official Sass docs](https://sass-lang.com/documentation/values/maps) to get started.
The `$utilities` map contains all our utilities and is later merged with your custom `$utilities` map, if present. The utility map contains a keyed list of utility groups which accept the following options:
| [`property`](#property) | **Required** | – | Name of the property, this can be a string or an array of strings (e.g., horizontal paddings or margins). |
| [`values`](#values) | **Required** | – | List of values, or a map if you don't want the class name to be the same as the value. If `null` is used as map key, `class` is not prepended to the class name. |
| [`class`](#class) | Optional | null | Name of the generated class. If not provided and `property` is an array of strings, `class` will default to the first element of the `property` array. If not provided and `property` is a string, the `values` keys are used for the `class` names. |
| [`css-var`](#css-variable-utilities) | Optional | `false` | Boolean to generate CSS variables instead of CSS rules. |
| [`css-variable-name`](#css-variable-utilities) | Optional | null | Custom un-prefixed name for the CSS variable inside the ruleset. |
| [`local-vars`](#local-css-variables) | Optional | null | Map of local CSS variables to generate in addition to the CSS rules. |
| [`state`](#states) | Optional | null | List of pseudo-class variants (e.g., `:hover` or `:focus`) to generate. |
| [`responsive`](#responsive) | Optional | `false` | Boolean indicating if responsive classes should be generated. |
| `rfs` | Optional | `false` | Boolean to enable [fluid rescaling with RFS]({{< docsref "/getting-started/rfs" >}}). |
| [`print`](#print) | Optional | `false` | Boolean indicating if print classes need to be generated. |
| `rtl` | Optional | `true` | Boolean indicating if utility should be kept in RTL. |
All utility variables are added to the `$utilities` variable within our `_utilities.scss` stylesheet. Each group of utilities looks something like this:
The required `property` key must be set for any utility, and it must contain a valid CSS property. This property is used in the generated utility's ruleset. When the `class` key is omitted, it also serves as the default class name. Consider the `text-decoration` utility:
Use the `values` key to specify which values for the specified `property` should be used in the generated class names and rules. Can be a list or map (set in the utilities or in a Sass variable).
As a list, like with [`text-decoration` utilities]({{< docsref "/utilities/text#text-decoration" >}}):
```scss
values: none underline line-through
```
As a map, like with [`opacity` utilities]({{< docsref "/utilities/opacity" >}}):
```scss
values: (
0: 0,
25: .25,
50: .5,
75: .75,
100: 1,
)
```
As a Sass variable that sets the list or map, as in our [`position` utilities]({{< docsref "/utilities/position" >}}):
```scss
values: $position-values
```
### Class
Use the `class` option to change the class prefix used in the compiled CSS. For example, to change from `.opacity-*` to `.o-*`:
Set the `css-var` boolean option to `true` and the API will generate local CSS variables for the given selector instead of the usual `property: value` rules. Add an optional `css-variable-name` to set a different CSS variable name than the class name.
Consider our `.text-opacity-*` utilities. If we add the `css-variable-name` option, we'll get a custom output.
Use the `local-vars` option to specify a Sass map that will generate local CSS variables within the utility class's ruleset. Please note that it may require additional work to consume those local CSS variables in the generated CSS rules. For example, consider our `.bg-*` utilities:
Use the `state` option to generate pseudo-class variations. Example pseudo-classes are `:hover` and `:focus`. When a list of states are provided, classnames are created for that pseudo-class. For example, to change opacity on hover, add `state: hover` and you'll get `.opacity-hover:hover` in your compiled CSS.
Need multiple pseudo-classes? Use a space-separated list of states: `state: hover focus`.
All utilities generated by the API include `!important` to ensure they override components and modifier classes as intended. You can toggle this setting globally with the `$enable-important-utilities` variable (defaults to `true`).
You may also want to refer to parts of the utilities configuration in your Sass code, the value of a specific utility especially. We provide getter functions to access those.
If your code declares a `$utilities` map before importing `bootstrap/scss/utilities`, it'll be merged with our default map. Add new keys to create your own utilities and override existing utilities by using the same key.
`utilities-add` and `utilities-remove` mixins let you add and remove utilities from the configuration. Adding an existing utility will completely override it.
`utilities-set-option` and `utilities-set-options` let you configure one or several options of a utility. `utilities-set-options` will merge the new options with the existing ones by default, but you can provide a third `$merge: false` argument to completely override them.
If you want to keep most of the default values for a utility, and just add, remove or update a few, replacing the `values` option can be a bit of a burden to maintain. `utilities-add-values` and `utilities-remove-values` mixins will help you make these targeted updates.
The `utilities-get-value` function let your grab a specific value of a utility. This can help you run some computations with it, either in Sass or with `calc()`. It also lets you access values that can be modified by other utilities, (like how `bg`, `text` and `border` can be affected by `bg-opacity`, `text-opacity` or `border-opacity` respectively).
You can enable responsive classes for an existing set of utilities that are not currently responsive by default. For example, to make the `border` classes responsive:
Missing v4 utilities, or used to another naming convention? The utilities API can be used to override the resulting `class` of a given utility—for example, to rename `.ms-*` utilities to oldish `.ml-*`:
Some edge cases make [RTL styling difficult](https://rtlstyling.com/posts/rtl-styling#common-things-that-might-not-work-for-rtl), such as line breaks in Arabic. Thus utilities can be dropped from RTL output by setting the `rtl` option to `false`:
This doesn't output anything in RTL, thanks to [the RTLCSS `remove` control directive](https://rtlcss.com/learn/usage-guide/control-directives/#remove).
