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Utility API

The utility API is a Sass-based tool to generate utility classes.

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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 of families classes with various options. If you're unfamiliar with Sass maps, read up on the official Sass docs to get started.

The $utilitiesmap contains all our utilities and is later merged with your custom $utilitiesmap, if present. The utility map contains a keyed list of utility groups which accept the following options:

Option	type	Description
`property`	Required	Name of the property, this can be a string or an array of strings (eg, horizontal paddings or margins).
`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, it isn't compiled.
`class`	optional	Variable for the class name if you don't want it to be the same as the property. In case you don't provide the `class`key and `property`key is an array of strings, the class name will be the first element of the `property`array.
`state`	optional	List of pseudo-class variants like `:hover`or `:focus`to generate for the utility. No default value.
`responsive`	optional	Boolean indicating if responsive classes need to be generated. `false`by default.
`rfs`	optional	Boolean to enable fluid rescaling. Have a look at the RFS page to find out how this works. `false`by default.
`print`	optional	Boolean indicating if print classes need to be generated. `false`by default.
`rtl`	optional	Boolean indicating if utility should be kept in RTL. `true`by default.

API explained

All utility variables are added to the $utilitiesvariable within our _utilities.scssstylesheet. Each group of utilities looks something like this:

$utilities: (
  "opacity": (
    property: opacity,
    values: (
      0: 0,
      25: .25,
      50: .5,
      75: .75,
      100: 1,
    )
  )
 );

Which outputs the following:

.opacity-0 { opacity: 0; }
.opacity-25 { opacity: .25; }
.opacity-50 { opacity: .5; }
.opacity-75 { opacity: .75; }
.opacity-100 { opacity: 1; }

custom class prefix

Use the classoption to change the class prefix used in the compiled CSS:

$utilities: (
  "opacity": (
    property: opacity,
    class: o,
    values: (
      0: 0,
      25: .25,
      50: .5,
      75: .75,
      100: 1,
    )
  )
 );

output:

.o-0 { opacity: 0; }
.o-25 { opacity: .25; }
.o-50 { opacity: .5; }
.o-75 { opacity: .75; }
.o-100 { opacity: 1; }

States

Use the stateoption to generate pseudo-class variations. Example pseudo-classes are :hoverand :focus. When a list of states are provided, classnames are created for that pseudo-class. For example, to change opacity on hover, add state: hoverand you'll get .opacity-hover:hoverin your compiled CSS.

Need multiple pseudo-classes? Use a space-separated list of states: state: hover focus.

$utilities: (
  "opacity": (
    property: opacity,
    class: opacity,
    state: hover,
    values: (
      0: 0,
      25: .25,
      50: .5,
      75: .75,
      100: 1,
    )
  )
);

output:

.opacity-0-hover:hover { opacity: 0 !important; }
.opacity-25-hover:hover { opacity: .25 !important; }
.opacity-50-hover:hover { opacity: .5 !important; }
.opacity-75-hover:hover { opacity: .75 !important; }
.opacity-100-hover:hover { opacity: 1 !important; }

Responsive utilities

Add the responsiveboolean to generate responsive utilities (eg, .opacity-md-25) across all breakpoints .

$utilities: (
  "opacity": (
    property: opacity,
    responsive: true,
    values: (
      0: 0,
      25: .25,
      50: .5,
      75: .75,
      100: 1,
    )
  )
 );

output:

.opacity-0 { opacity: 0 !important; }
.opacity-25 { opacity: .25 !important; }
.opacity-50 { opacity: .5 !important; }
.opacity-75 { opacity: .75 !important; }
.opacity-100 { opacity: 1 !important; }

@media (min-width: 576px) {
  .opacity-sm-0 { opacity: 0 !important; }
  .opacity-sm-25 { opacity: .25 !important; }
  .opacity-sm-50 { opacity: .5 !important; }
  .opacity-sm-75 { opacity: .75 !important; }
  .opacity-sm-100 { opacity: 1 !important; }
}

@media (min-width: 768px) {
  .opacity-md-0 { opacity: 0 !important; }
  .opacity-md-25 { opacity: .25 !important; }
  .opacity-md-50 { opacity: .5 !important; }
  .opacity-md-75 { opacity: .75 !important; }
  .opacity-md-100 { opacity: 1 !important; }
}

@media (min-width: 992px) {
  .opacity-lg-0 { opacity: 0 !important; }
  .opacity-lg-25 { opacity: .25 !important; }
  .opacity-lg-50 { opacity: .5 !important; }
  .opacity-lg-75 { opacity: .75 !important; }
  .opacity-lg-100 { opacity: 1 !important; }
}

@media (min-width: 1200px) {
  .opacity-xl-0 { opacity: 0 !important; }
  .opacity-xl-25 { opacity: .25 !important; }
  .opacity-xl-50 { opacity: .5 !important; }
  .opacity-xl-75 { opacity: .75 !important; }
  .opacity-xl-100 { opacity: 1 !important; }
}

@media (min-width: 1400px) {
  .opacity-xxl-0 { opacity: 0 !important; }
  .opacity-xxl-25 { opacity: .25 !important; }
  .opacity-xxl-50 { opacity: .5 !important; }
  .opacity-xxl-75 { opacity: .75 !important; }
  .opacity-xxl-100 { opacity: 1 !important; }
}

Changing utilities

Override existing utilities by using the same key. For example, if you want additional responsive overflow utility classes, you can do this:

$utilities: (
  "overflow": (
    responsive: true,
    property: overflow,
    values: visible hidden scroll auto,
  ),
);

Print utilities

Enabling the printoption will also generate utility classes for print, which are only applied within the @media print { ... }media query.

$utilities: (
  "opacity": (
    property: opacity,
    print: true,
    values: (
      0: 0,
      25: .25,
      50: .5,
      75: .75,
      100: 1,
    )
  )
 );

output:

.opacity-0 { opacity: 0 !important; }
.opacity-25 { opacity: .25 !important; }
.opacity-50 { opacity: .5 !important; }
.opacity-75 { opacity: .75 !important; }
.opacity-100 { opacity: 1 !important; }

@media print {
  .opacity-print-0 { opacity: 0 !important; }
  .opacity-print-25 { opacity: .25 !important; }
  .opacity-print-50 { opacity: .5 !important; }
  .opacity-print-75 { opacity: .75 !important; }
  .opacity-print-100 { opacity: 1 !important; }
}

Importance

All utilities generated by the API include !importantto ensure they override components and modifier classes as intended. You can toggle this setting globally with the $enable-important-utilitiesvariable (defaults to true).

Using the API

Now that you're familiar with how the utilities API works, learn how to add your own custom classes and modify our default utilities.

Add utilities

New utilities can be added to the default $utilitiesmap with a map-merge. Make sure our required Sass files and _utilities.scssare imported first, then use the map-mergeto add your additional utilities. For example, here's how to add a responsive cursorutility with three values.

@import "bootstrap/scss/functions";
@import "bootstrap/scss/variables";
@import "bootstrap/scss/utilities";

$utilities: map-merge(
  $utilities,
  (
    "cursor": (
      property: cursor,
      class: cursor,
      responsive: true,
      values: auto pointer grab,
    )
  )
);

Modify utilities

Modify existing utilities in the default $utilitiesmap with map-getand map-mergefunctions. In the example below, we're adding an additional value to the widthutilities. Start with an initial map-mergeand then specify which utility you want to modify. From there, fetch the nested "width"map with map-getto access and modify the utility's options and values.

@import "bootstrap/scss/functions";
@import "bootstrap/scss/variables";
@import "bootstrap/scss/utilities";

$utilities: map-merge(
  $utilities,
  (
    "width": map-merge(
      map-get($utilities, "width"),
      (
        values: map-merge(
          map-get(map-get($utilities, "width"), "values"),
          (10: 10%),
        ),
      ),
    ),
  )
);

Enable responsive

You can enable responsive classes for an existing set of utilities that are not currently responsive by default. For example, to make the borderclasses responsive:

@import "bootstrap/scss/functions";
@import "bootstrap/scss/variables";
@import "bootstrap/scss/utilities";

$utilities: map-merge(
  $utilities, (
    "border": map-merge(
      map-get($utilities, "border"),
      ( responsive: true ),
    ),
  )
);

This will now generate responsive variations of .borderand .border-0for each breakpoint. Your generated CSS will look like this:

.border { ... }
.border-0 { ... }

@media (min-width: 576px) {
  .border-sm { ... }
  .border-sm-0 { ... }
}

@media (min-width: 768px) {
  .border-md { ... }
  .border-md-0 { ... }
}

@media (min-width: 992px) {
  .border-lg { ... }
  .border-lg-0 { ... }
}

@media (min-width: 1200px) {
  .border-xl { ... }
  .border-xl-0 { ... }
}

@media (min-width: 1400px) {
  .border-xxl { ... }
  .border-xxl-0 { ... }
}

Rename utilities

Missing v4 utilities, or used to another naming convention? The utilities API can be used to override the resulting classof a given utility—for example, to rename .ms-*utilities to oldish .ml-*:

@import "bootstrap/scss/functions";
@import "bootstrap/scss/variables";
@import "bootstrap/scss/utilities";

$utilities: map-merge(
  $utilities, (
    "margin-start": map-merge(
      map-get($utilities, "margin-start"),
      ( class: ml ),
    ),
  )
);

Remove utilities

Remove any of the default utilities by setting the group key to null. For example, to remove all our widthutilities, create a $utilities map-mergeand add "width": nullwithin.

@import "bootstrap/scss/functions";
@import "bootstrap/scss/variables";
@import "bootstrap/scss/utilities";

$utilities: map-merge(
  $utilities,
  (
    "width": null
  )
);

Remove utility in RTL

Some edge cases make RTL styling difficult , such as line breaks in Arabic. Thus utilities can be dropped from RTL output by setting the rtloption to false:

$utilities: (
  "word-wrap": (
    property: word-wrap word-break,
    class: text,
    values: (break: break-word),
    rtl: false
  ),
);

output:

/* rtl:begin:remove */
.text-break {
  word-wrap: break-word !important;
  word-break: break-word !important;
}
/* rtl:end:remove */

This doesn't output anything in RTL, thanks to the RTLCSS removecontrol directive .