What are utility classes in bootstrap?

For faster mobile-friendly and responsive development, Bootstrap includes dozens of utility classes for showing, hiding, aligning, and spacing content.

Changing display

Use our display utilities for responsively toggling common values of the display property. Mix it with our grid system, content, or components to show or hide them across specific viewports.

Flexbox options

Bootstrap 4 is built with flexbox, but not every element’s display has been changed to display: flex as this would add many unnecessary overrides and unexpectedly change key browser behaviors. Most of our components are built with flexbox enabled.

Should you need to add display: flex to an element, do so with .d-flex or one of the responsive variants (e.g., .d-sm-flex). You’ll need this class or display value to allow the use of our extra flexbox utilities for sizing, alignment, spacing, and more.

Margin and padding

Use the margin and padding spacing utilities to control how elements and components are spaced and sized. Bootstrap 4 includes a five-level scale for spacing utilities, based on a 1rem value default $spacer variable. Choose values for all viewports (e.g., .mr-3 for margin-right: 1rem), or pick responsive variants to target specific viewports (e.g., .mr-md-3 for margin-right: 1rem starting at the md breakpoint).

Toggle visibility

When toggling display isn’t needed, you can toggle the visibility of an element with our visibility utilities. Invisible elements will still affect the layout of the page, but are visually hidden from visitors.

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 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:

API explained

All utility variables are added to the $utilities variable within our _utilities.scss stylesheet. 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 class option 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 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.

$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 responsive boolean to generate responsive utilities (e.g., .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 print option 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 !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).

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 $utilities map with a map-merge. Make sure our required Sass files and _utilities.scss are imported first, then use the map-merge to add your additional utilities. For example, here’s how to add a responsive cursor utility 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 $utilities map with map-get and map-merge functions. In the example below, we’re adding an additional value to the width utilities. Start with an initial map-merge and then specify which utility you want to modify. From there, fetch the nested "width" map with map-get to 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 border classes 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 .border and .border-0 for 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 class of 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 width utilities, create a $utilities map-merge and add "width": null within.

@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 rtl option 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 remove control directive.

How do I use Bootstrap utilities?

What are responsive utility classes in bootstrap?

What is a utility class in CSS?

What are the different classes of bootstrap?