	Chrome	Firefox	Safari	Android Browser & WebView	Microsoft Edge
Android	Supported	Supported	N/A	Android v5.0+ supported	Supported
iOS	Supported	Supported	Supported	N/A	Supported
Windows 10 Mobile	N/A	N/A	N/A	N/A	Supported

	Chrome	Firefox	Internet Explorer	Microsoft Edge	Opera	Safari
Mac	Supported	Supported	N/A	Supported	Supported	Supported
Windows	Supported	Supported	Supported, IE10+	Supported	Supported	Not supported

Task	Description
`npm run dist`	`npm run dist` creates the `/dist/` directory with compiled files. Uses Sass, Autoprefixer, and terser.
`npm test`	Runs tests locally after running `npm run dist`
`npm run docs-serve`	Builds and runs the documentation locally.

CSS files	Layout	Content	Components	Utilities
+ `bootstrap.css` + `bootstrap.min.css` +	Included	Included	Included	Included
+ `bootstrap-grid.css` + `bootstrap-grid.min.css` +	Only grid system	Not included	Not included	Only flex utilities
+ `bootstrap-reboot.css` + `bootstrap-reboot.min.css` +	Not included	Only Reboot	Not included	Not included

JS files	Popper	jQuery
+ `bootstrap.bundle.js` + `bootstrap.bundle.min.js` +	Included	Not included
+ `bootstrap.js` + `bootstrap.min.js` +	Not included	Not included

+ View on GitHub +

JavaScript

Bring Bootstrap to life with our optional JavaScript plugins built on jQuery. Learn about each plugin, our data and programmatic API options, and more.

+ + +

Individual or compiled

Plugins can be included individually (using Bootstrap’s individual js/dist/*.js), or all at once using bootstrap.js or the minified bootstrap.min.js (don’t include both).

If you use a bundler (Webpack, Rollup…), you can use /js/dist/*.js files which are UMD ready.

Dependencies

Some plugins and CSS components depend on other plugins. If you include plugins individually, make sure to check for these dependencies in the docs. Also note that all plugins depend on jQuery (this means jQuery must be included before the plugin files). Consult our package.json to see which versions of jQuery are supported.

Our dropdowns, popovers and tooltips also depend on Popper.js.

Data attributes

Nearly all Bootstrap plugins can be enabled and configured through HTML alone with data attributes (our preferred way of using JavaScript functionality). Be sure to only use one set of data attributes on a single element (e.g., you cannot trigger a tooltip and modal from the same button.)

However, in some situations it may be desirable to disable this functionality. To disable the data attribute API, unbind all events on the document namespaced with data-api like so:

$(document).off('.data-api')
+

Alternatively, to target a specific plugin, just include the plugin’s name as a namespace along with the data-api namespace like this:

$(document).off('.alert.data-api')
+

Selectors

Currently to query DOM elements we use the native methods querySelector and querySelectorAll for performance reasons, so you have to use valid selectors. +If you use special selectors, for example: collapse:Example be sure to escape them. +

+ +

Events

Bootstrap provides custom events for most plugins' unique actions. Generally, these come in an infinitive and past participle form - where the infinitive (ex. show) is triggered at the start of an event, and its past participle form (ex. shown) is triggered on the completion of an action.

All infinitive events provide preventDefault() functionality. This provides the ability to stop the execution of an action before it starts. Returning false from an event handler will also automatically call preventDefault().

$('#myModal').on('show.bs.modal', function (event) {
+  if (!data) {
+    return event.preventDefault() // stops modal from being shown
+  }
+})
+

Programmatic API

We also believe you should be able to use all Bootstrap plugins purely through the JavaScript API. All public APIs are single, chainable methods, and return the collection acted upon.

$('.btn.danger').button('toggle').addClass('fat')
+

All methods should accept an optional options object, a string which targets a particular method, or nothing (which initiates a plugin with default behavior):

$('#myModal').modal() // initialized with defaults
+$('#myModal').modal({ keyboard: false }) // initialized with no keyboard
+$('#myModal').modal('show') // initializes and invokes show immediately
+

Each plugin also exposes its raw constructor on a Constructor property: $.fn.popover.Constructor. If you’d like to get a particular plugin instance, retrieve it directly from an element: $('[rel="popover"]').data('popover').

Asynchronous functions and transitions

All programmatic API methods are asynchronous and return to the caller once the transition is started but before it ends.

In order to execute an action once the transition is complete, you can listen to the corresponding event.

$('#myCollapse').on('shown.bs.collapse', function (event) {
+  // Action to execute once the collapsible area is expanded
+})
+

In addition a method call on a transitioning component will be ignored.

$('#myCarousel').on('slid.bs.carousel', function (event) {
+  $('#myCarousel').carousel('2') // Will slide to the slide 2 as soon as the transition to slide 1 is finished
+})
+
+$('#myCarousel').carousel('1') // Will start sliding to the slide 1 and returns to the caller
+$('#myCarousel').carousel('2') // !! Will be ignored, as the transition to the slide 1 is not finished !!
+

Default settings

You can change the default settings for a plugin by modifying the plugin’s Constructor.Default object:

// changes default for the modal plugin's `keyboard` option to false
+$.fn.modal.Constructor.Default.keyboard = false
+

No conflict

Sometimes it is necessary to use Bootstrap plugins with other UI frameworks. In these circumstances, namespace collisions can occasionally occur. If this happens, you may call .noConflict on the plugin you wish to revert the value of.

var bootstrapButton = $.fn.button.noConflict() // return $.fn.button to previously assigned value
+$.fn.bootstrapBtn = bootstrapButton // give $().bootstrapBtn the Bootstrap functionality
+

Version numbers

The version of each of Bootstrap’s jQuery plugins can be accessed via the VERSION property of the plugin’s constructor. For example, for the tooltip plugin:

$.fn.tooltip.Constructor.VERSION // => "4.6.0"
+

No special fallbacks when JavaScript is disabled

Bootstrap’s plugins don’t fall back particularly gracefully when JavaScript is disabled. If you care about the user experience in this case, use <noscript> to explain the situation (and how to re-enable JavaScript) to your users, and/or add your own custom fallbacks.

Third-party libraries

Bootstrap does not officially support third-party JavaScript libraries like Prototype or jQuery UI. Despite .noConflict and namespaced events, there may be compatibility problems that you need to fix on your own. +

+ +

Util

All Bootstrap’s JavaScript files depend on util.js and it has to be included alongside the other JavaScript files. If you’re using the compiled (or minified) bootstrap.js, there is no need to include this—it’s already there.

util.js includes utility functions and a basic helper for transitionEnd events as well as a CSS transition emulator. It’s used by the other plugins to check for CSS transition support and to catch hanging transitions.

Sanitizer

Tooltips and Popovers use our built-in sanitizer to sanitize options which accept HTML.

The default whiteList value is the following:

var ARIA_ATTRIBUTE_PATTERN = /^aria-[\w-]*$/i
+var DefaultWhitelist = {
+  // Global attributes allowed on any supplied element below.
+  '*': ['class', 'dir', 'id', 'lang', 'role', ARIA_ATTRIBUTE_PATTERN],
+  a: ['target', 'href', 'title', 'rel'],
+  area: [],
+  b: [],
+  br: [],
+  col: [],
+  code: [],
+  div: [],
+  em: [],
+  hr: [],
+  h1: [],
+  h2: [],
+  h3: [],
+  h4: [],
+  h5: [],
+  h6: [],
+  i: [],
+  img: ['src', 'srcset', 'alt', 'title', 'width', 'height'],
+  li: [],
+  ol: [],
+  p: [],
+  pre: [],
+  s: [],
+  small: [],
+  span: [],
+  sub: [],
+  sup: [],
+  strong: [],
+  u: [],
+  ul: []
+}
+

If you want to add new values to this default whiteList you can do the following:

var myDefaultWhiteList = $.fn.tooltip.Constructor.Default.whiteList
+
+// To allow table elements
+myDefaultWhiteList.table = []
+
+// To allow td elements and data-option attributes on td elements
+myDefaultWhiteList.td = ['data-option']
+
+// You can push your custom regex to validate your attributes.
+// Be careful about your regular expressions being too lax
+var myCustomRegex = /^data-my-app-[\w-]+/
+myDefaultWhiteList['*'].push(myCustomRegex)
+

If you want to bypass our sanitizer because you prefer to use a dedicated library, for example DOMPurify, you should do the following:

$('#yourTooltip').tooltip({
+  sanitizeFn: function (content) {
+    return DOMPurify.sanitize(content)
+  }
+})
+

+ View on GitHub +

Theming Bootstrap

Customize Bootstrap 4 with our new built-in Sass variables for global style preferences for easy theming and component changes.

+ + +

Introduction

In Bootstrap 3, theming was largely driven by variable overrides in LESS, custom CSS, and a separate theme stylesheet that we included in our dist files. With some effort, one could completely redesign the look of Bootstrap 3 without touching the core files. Bootstrap 4 provides a familiar, but slightly different approach.

Now, theming is accomplished by Sass variables, Sass maps, and custom CSS. There’s no more dedicated theme stylesheet; instead, you can enable the built-in theme to add gradients, shadows, and more.

Sass

Utilize our source Sass files to take advantage of variables, maps, mixins, and more when compiling Sass using your own asset pipeline.

File structure

Whenever possible, avoid modifying Bootstrap’s core files. For Sass, that means creating your own stylesheet that imports Bootstrap so you can modify and extend it. Assuming you’re using a package manager like npm, you’ll have a file structure that looks like this:

your-project/
+├── scss
+│   └── custom.scss
+└── node_modules/
+    └── bootstrap
+        ├── js
+        └── scss
+

If you’ve downloaded our source files and aren’t using a package manager, you’ll want to manually setup something similar to that structure, keeping Bootstrap’s source files separate from your own.

your-project/
+├── scss
+│   └── custom.scss
+└── bootstrap/
+    ├── js
+    └── scss
+

Importing

In your custom.scss, you’ll import Bootstrap’s source Sass files. You have two options: include all of Bootstrap, or pick the parts you need. We encourage the latter, though be aware there are some requirements and dependencies across our components. You also will need to include some JavaScript for our plugins.

// Custom.scss
+// Option A: Include all of Bootstrap
+
+@import "../node_modules/bootstrap/scss/bootstrap";
+
+// Add custom code after this
+

// Custom.scss
+// Option B: Include parts of Bootstrap
+
+// Required
+@import "../node_modules/bootstrap/scss/functions";
+@import "../node_modules/bootstrap/scss/variables";
+@import "../node_modules/bootstrap/scss/mixins";
+
+// Include custom variable default overrides here
+
+// Optional
+@import "../node_modules/bootstrap/scss/reboot";
+@import "../node_modules/bootstrap/scss/type";
+@import "../node_modules/bootstrap/scss/images";
+@import "../node_modules/bootstrap/scss/code";
+@import "../node_modules/bootstrap/scss/grid";
+

With that setup in place, you can begin to modify any of the Sass variables and maps in your custom.scss. You can also start to add parts of Bootstrap under the // Optional section as needed. We suggest using the full import stack from our bootstrap.scss file as your starting point.

Variable defaults

Every Sass variable in Bootstrap includes the !default flag allowing you to override the variable’s default value in your own Sass without modifying Bootstrap’s source code. Copy and paste variables as needed, modify their values, and remove the !default flag. If a variable has already been assigned, then it won’t be re-assigned by the default values in Bootstrap.

You will find the complete list of Bootstrap’s variables in scss/_variables.scss. Some variables are set to null, these variables don’t output the property unless they are overridden in your configuration.

Variable overrides must come after our functions, variables, and mixins are imported, but before the rest of the imports.

Here’s an example that changes the background-color and color for the <body> when importing and compiling Bootstrap via npm:

// Required
+@import "../node_modules/bootstrap/scss/functions";
+@import "../node_modules/bootstrap/scss/variables";
+@import "../node_modules/bootstrap/scss/mixins";
+
+// Your variable overrides
+$body-bg: #000;
+$body-color: #111;
+
+// Bootstrap and its default variables
+
+// Optional
+@import "../node_modules/bootstrap/scss/root";
+@import "../node_modules/bootstrap/scss/reboot";
+@import "../node_modules/bootstrap/scss/type";
+// etc
+

Repeat as necessary for any variable in Bootstrap, including the global options below.

+Get started with Bootstrap via npm with our starter project! Head to the twbs/bootstrap-npm-starter template repository to see how to build and customize Bootstrap in your own npm project. Includes Sass compiler, Autoprefixer, Stylelint, PurgeCSS, and Bootstrap Icons. +

+ +

Maps and loops

Bootstrap 4 includes a handful of Sass maps, key value pairs that make it easier to generate families of related CSS. We use Sass maps for our colors, grid breakpoints, and more. Just like Sass variables, all Sass maps include the !default flag and can be overridden and extended.

Some of our Sass maps are merged into empty ones by default. This is done to allow easy expansion of a given Sass map, but comes at the cost of making removing items from a map slightly more difficult.

Modify map

To modify an existing color in our $theme-colors map, add the following to your custom Sass file:

$theme-colors: (
+  "primary": #0074d9,
+  "danger": #ff4136
+);
+

Add to map

To add a new color to $theme-colors, add the new key and value:

$theme-colors: (
+  "custom-color": #900
+);
+

Remove from map

To remove colors from $theme-colors, or any other map, use map-remove. Be aware you must insert it between our requirements and options:

// Required
+@import "../node_modules/bootstrap/scss/functions";
+@import "../node_modules/bootstrap/scss/variables";
+@import "../node_modules/bootstrap/scss/mixins";
+
+$theme-colors: map-remove($theme-colors, "info", "light", "dark");
+
+// Optional
+@import "../node_modules/bootstrap/scss/root";
+@import "../node_modules/bootstrap/scss/reboot";
+@import "../node_modules/bootstrap/scss/type";
+...
+

Required keys

Bootstrap assumes the presence of some specific keys within Sass maps as we used and extend these ourselves. As you customize the included maps, you may encounter errors where a specific Sass map’s key is being used.

For example, we use the primary, success, and danger keys from $theme-colors for links, buttons, and form states. Replacing the values of these keys should present no issues, but removing them may cause Sass compilation issues. In these instances, you’ll need to modify the Sass code that makes use of those values.

Functions

Bootstrap utilizes several Sass functions, but only a subset are applicable to general theming. We’ve included three functions for getting values from the color maps:

@function color($key: "blue") {
+  @return map-get($colors, $key);
+}
+
+@function theme-color($key: "primary") {
+  @return map-get($theme-colors, $key);
+}
+
+@function gray($key: "100") {
+  @return map-get($grays, $key);
+}
+

These allow you to pick one color from a Sass map much like how you’d use a color variable from v3.

.custom-element {
+  color: gray("100");
+  background-color: theme-color("dark");
+}
+

We also have another function for getting a particular level of color from the $theme-colors map. Negative level values will lighten the color, while higher levels will darken.

@function theme-color-level($color-name: "primary", $level: 0) {
+  $color: theme-color($color-name);
+  $color-base: if($level > 0, #000, #fff);
+  $level: abs($level);
+
+  @return mix($color-base, $color, $level * $theme-color-interval);
+}
+

In practice, you’d call the function and pass in two parameters: the name of the color from $theme-colors (e.g., primary or danger) and a numeric level.

.custom-element {
+  color: theme-color-level(primary, -10);
+}
+

Additional functions could be added in the future or your own custom Sass to create level functions for additional Sass maps, or even a generic one if you wanted to be more verbose.

Color contrast

An additional function we include in Bootstrap is the color contrast function, color-yiq. It utilizes the YIQ color space to automatically return a light (#fff) or dark (#111) contrast color based on the specified base color. This function is especially useful for mixins or loops where you’re generating multiple classes.

For example, to generate color swatches from our $theme-colors map:

@each $color, $value in $theme-colors {
+  .swatch-#{$color} {
+    color: color-yiq($value);
+  }
+}
+

It can also be used for one-off contrast needs:

.custom-element {
+  color: color-yiq(#000); // returns `color: #fff`
+}
+

You can also specify a base color with our color map functions:

.custom-element {
+  color: color-yiq(theme-color("dark")); // returns `color: #fff`
+}
+

Escape SVG

We use the escape-svg function to escape the <, > and # characters for SVG background images. These characters need to be escaped to properly render the background images in IE. When using the escape-svg function, data URIs must be quoted.

Add and Subtract functions

We use the add and subtract functions to wrap the CSS calc function. The primary purpose of these functions is to avoid errors when a “unitless” 0 value is passed into a calc expression. Expressions like calc(10px - 0) will return an error in all browsers, despite being mathematically correct.

Example where the calc is valid:

$border-radius: .25rem;
+$border-width: 1px;
+
+.element {
+  // Output calc(.25rem - 1px) is valid
+  border-radius: calc($border-radius - $border-width);
+}
+
+.element {
+  // Output the same calc(.25rem - 1px) as above
+  border-radius: subtract($border-radius, $border-width);
+}
+

Example where the calc is invalid:

$border-radius: .25rem;
+$border-width: 0;
+
+.element {
+  // Output calc(.25rem - 0) is invalid
+  border-radius: calc($border-radius - $border-width);
+}
+
+.element {
+  // Output .25rem
+  border-radius: subtract($border-radius, $border-width);
+}
+

Sass options

Customize Bootstrap 4 with our built-in custom variables file and easily toggle global CSS preferences with new $enable-* Sass variables. Override a variable’s value and recompile with npm run test as needed.

You can find and customize these variables for key global options in Bootstrap’s scss/_variables.scss file.

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

Variable	Values	Description
`$spacer`	`1rem` (default), or any value > 0	Specifies the default spacer value to programmatically generate our spacer utilities.
`$enable-rounded`	`true` (default) or `false`	Enables predefined `border-radius` styles on various components.
`$enable-shadows`	`true` or `false` (default)	Enables predefined decorative `box-shadow` styles on various components. Does not affect `box-shadow`s used for focus states.
`$enable-gradients`	`true` or `false` (default)	Enables predefined gradients via `background-image` styles on various components.
`$enable-transitions`	`true` (default) or `false`	Enables predefined `transition`s on various components.
`$enable-prefers-reduced-motion-media-query`	`true` (default) or `false`	Enables the `prefers-reduced-motion` media query, which suppresses certain animations/transitions based on the users' browser/operating system preferences.
`$enable-hover-media-query`	`true` or `false` (default)	Deprecated
`$enable-grid-classes`	`true` (default) or `false`	Enables the generation of CSS classes for the grid system (e.g., `.container`, `.row`, `.col-md-1`, etc.).
`$enable-caret`	`true` (default) or `false`	Enables pseudo element caret on `.dropdown-toggle`.
`$enable-pointer-cursor-for-buttons`	`true` (default) or `false`	Add “hand” cursor to non-disabled button elements.
`$enable-print-styles`	`true` (default) or `false`	Enables styles for optimizing printing.
`$enable-responsive-font-sizes`	`true` or `false` (default)	Enables responsive font sizes.
`$enable-validation-icons`	`true` (default) or `false`	Enables `background-image` icons within textual inputs and some custom forms for validation states.
`$enable-deprecation-messages`	`true` or `false` (default)	Set to `true` to show warnings when using any of the deprecated mixins and functions that are planned to be removed in `v5`.

Color

Many of Bootstrap’s various components and utilities are built through a series of colors defined in a Sass map. This map can be looped over in Sass to quickly generate a series of rulesets.

All colors

All colors available in Bootstrap 4, are available as Sass variables and a Sass map in scss/_variables.scss file. This will be expanded upon in subsequent minor releases to add additional shades, much like the grayscale palette we already include.

+ +

+ $blue + #007bff +

+ +

+ $indigo + #6610f2 +

+ +

+ $purple + #6f42c1 +

+ +

+ $pink + #e83e8c +

+ +

+ $red + #dc3545 +

+ +

+ $orange + #fd7e14 +

+ +

+ $yellow + #ffc107 +

+ +

+ $green + #28a745 +

+ +

+ $teal + #20c997 +

+ +

+ $cyan + #17a2b8 +

+ +

Here’s how you can use these in your Sass:

// With variable
+.alpha { color: $purple; }
+
+// From the Sass map with our `color()` function
+.beta { color: color("purple"); }
+

Color utility classes are also available for setting color and background-color.

+In the future, we’ll aim to provide Sass maps and variables for shades of each color as we’ve done with the grayscale colors below. +

+ +

Theme colors

We use a subset of all colors to create a smaller color palette for generating color schemes, also available as Sass variables and a Sass map in Bootstrap’s scss/_variables.scss file.

+ +

+ $primary + #007bff +

+ +

+ $secondary + #868e96 +

+ +

+ $success + #28a745 +

+ +

+ $danger + #dc3545 +

+ +

+ $warning + #ffc107 +

+ +

+ $info + #17a2b8 +

+ +

+ $light + #f8f9fa +

+ +

+ $dark + #343a40 +

+ +

Grays

An expansive set of gray variables and a Sass map in scss/_variables.scss for consistent shades of gray across your project. Note that these are “cool grays”, which tend towards a subtle blue tone, rather than neutral grays.

+ +

+ $gray-100 + #f8f9fa +

+ +

+ $gray-200 + #e9ecef +

+ +

+ $gray-300 + #dee2e6 +

+ +

+ $gray-400 + #ced4da +

+ +

+ $gray-500 + #adb5bd +

+ +

+ $gray-600 + #6c757d +

+ +

+ $gray-700 + #495057 +

+ +

+ $gray-800 + #343a40 +

+ +

+ $gray-900 + #212529 +

+ +

Within scss/_variables.scss, you’ll find Bootstrap’s color variables and Sass map. Here’s an example of the $colors Sass map:

$colors: (
+  "blue": $blue,
+  "indigo": $indigo,
+  "purple": $purple,
+  "pink": $pink,
+  "red": $red,
+  "orange": $orange,
+  "yellow": $yellow,
+  "green": $green,
+  "teal": $teal,
+  "cyan": $cyan,
+  "white": $white,
+  "gray": $gray-600,
+  "gray-dark": $gray-800
+) !default;
+

Add, remove, or modify values within the map to update how they’re used in many other components. Unfortunately at this time, not every component utilizes this Sass map. Future updates will strive to improve upon this. Until then, plan on making use of the ${color} variables and this Sass map.

Components

Many of Bootstrap’s components and utilities are built with @each loops that iterate over a Sass map. This is especially helpful for generating variants of a component by our $theme-colors and creating responsive variants for each breakpoint. As you customize these Sass maps and recompile, you’ll automatically see your changes reflected in these loops.

Modifiers

Many of Bootstrap’s components are built with a base-modifier class approach. This means the bulk of the styling is contained to a base class (e.g., .btn) while style variations are confined to modifier classes (e.g., .btn-danger). These modifier classes are built from the $theme-colors map to make customizing the number and name of our modifier classes.

Here are two examples of how we loop over the $theme-colors map to generate modifiers to the .alert component and all our .bg-* background utilities.

// Generate alert modifier classes
+@each $color, $value in $theme-colors {
+  .alert-#{$color} {
+    @include alert-variant(theme-color-level($color, -10), theme-color-level($color, -9), theme-color-level($color, 6));
+  }
+}
+
+// Generate `.bg-*` color utilities
+@each $color, $value in $theme-colors {
+  @include bg-variant('.bg-#{$color}', $value);
+}
+

Responsive

These Sass loops aren’t limited to color maps, either. You can also generate responsive variations of your components or utilities. Take for example our responsive text alignment utilities where we mix an @each loop for the $grid-breakpoints Sass map with a media query include.

@each $breakpoint in map-keys($grid-breakpoints) {
+  @include media-breakpoint-up($breakpoint) {
+    $infix: breakpoint-infix($breakpoint, $grid-breakpoints);
+
+    .text#{$infix}-left   { text-align: left !important; }
+    .text#{$infix}-right  { text-align: right !important; }
+    .text#{$infix}-center { text-align: center !important; }
+  }
+}
+

Should you need to modify your $grid-breakpoints, your changes will apply to all the loops iterating over that map.

CSS variables

Bootstrap 4 includes around two dozen CSS custom properties (variables) in its compiled CSS. These provide easy access to commonly used values like our theme colors, breakpoints, and primary font stacks when working in your browser’s Inspector, a code sandbox, or general prototyping.

Available variables

Here are the variables we include (note that the :root is required). They’re located in our _root.scss file.

:root {
+  --blue: #007bff;
+  --indigo: #6610f2;
+  --purple: #6f42c1;
+  --pink: #e83e8c;
+  --red: #dc3545;
+  --orange: #fd7e14;
+  --yellow: #ffc107;
+  --green: #28a745;
+  --teal: #20c997;
+  --cyan: #17a2b8;
+  --white: #fff;
+  --gray: #6c757d;
+  --gray-dark: #343a40;
+  --primary: #007bff;
+  --secondary: #6c757d;
+  --success: #28a745;
+  --info: #17a2b8;
+  --warning: #ffc107;
+  --danger: #dc3545;
+  --light: #f8f9fa;
+  --dark: #343a40;
+  --breakpoint-xs: 0;
+  --breakpoint-sm: 576px;
+  --breakpoint-md: 768px;
+  --breakpoint-lg: 992px;
+  --breakpoint-xl: 1200px;
+  --font-family-sans-serif: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", "Liberation Sans", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
+  --font-family-monospace: SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
+}
+

Examples

CSS variables offer similar flexibility to Sass’s variables, but without the need for compilation before being served to the browser. For example, here we’re resetting our page’s font and link styles with CSS variables.

body {
+  font: 1rem/1.5 var(--font-family-sans-serif);
+}
+a {
+  color: var(--blue);
+}
+

Breakpoint variables

While we originally included breakpoints in our CSS variables (e.g., --breakpoint-md), these are not supported in media queries, but they can still be used within rulesets in media queries. These breakpoint variables remain in the compiled CSS for backward compatibility given they can be utilized by JavaScript. Learn more in the spec.

Here’s an example of what’s not supported:

@media (min-width: var(--breakpoint-sm)) {
+  ...
+}
+

And here’s an example of what is supported:

@media (min-width: 768px) {
+  .custom-element {
+    color: var(--primary);
+  }
+}
+

Accessibility

Overview and Limitations

Structural markup

Interactive components

Color contrast

Visually hidden content

Reduced motion

Additional resources

Best practices

General outline

Browsers and devices

Supported browsers

Mobile devices

Desktop browsers

Internet Explorer

Modals and dropdowns on mobile

Overflow and scrolling

iOS text fields and scrolling

Navbar Dropdowns

Browser zooming

Sticky :hover/:focus on iOS

Printing

Android stock browser

Select menu

Validators

Build tools

Tooling setup

Using npm scripts

Sass

Autoprefixer

Local documentation

Troubleshooting

Contents

Precompiled Bootstrap

CSS files

JS files

Bootstrap source code

Download

Compiled CSS and JS

Source files

Examples

jsDelivr

Package managers

npm

yarn

RubyGems

Composer

NuGet

Introduction

Quick start

CSS

JS

Bundle

Separate

Components

Starter template

Important globals

HTML5 doctype

Responsive meta tag

Box-sizing

Reboot

Community

CSPs and embedded SVGs

JavaScript

Individual or compiled

Dependencies

Data attributes

Selectors

Events

Programmatic API

Asynchronous functions and transitions

Default settings

No conflict

Version numbers

No special fallbacks when JavaScript is disabled

Third-party libraries

Util

Sanitizer

Theming Bootstrap

Introduction

Sticky `:hover`/`:focus` on iOS