- Added [new Customize section](https://getbootstrap.com/docs/5.1/customize/overview/), replacing [v4's Theming page](https://getbootstrap.com/docs/4.6/getting-started/theming/), with new details on Sass, global configuration options, color schemes, CSS variables, and more.
- Reorganized all form documentation into [new Forms section](https://getbootstrap.com/docs/5.1/forms/overview/), breaking apart the content into more focused pages.
- Similarly, updated [the Layout section](https://getbootstrap.com/docs/5.1/layout/breakpoints/), to flesh out grid content more clearly.
- We've ditched the default Sass map merges to make it easier to remove redundant values. Keep in mind you now have to define all values in the Sass maps like `$theme-colors`. Check out how to deal with [Sass maps]({{< docsref "/customize/sass#maps-and-loops" >}}).
-<spanclass="badge bg-danger">Breaking</span> Renamed `color-yiq()` function and related variables to `color-contrast()` as it's no longer related to YIQ colorspace. [See #30168.](https://github.com/twbs/bootstrap/pull/30168/)
-`$yiq-contrasted-threshold` is renamed to `$min-contrast-ratio`.
-`$yiq-text-dark` and `$yiq-text-light` are respectively renamed to `$color-contrast-dark` and `$color-contrast-light`.
-<spanclass="badge bg-danger">Breaking</span> Media query mixins parameters have changed for a more logical approach.
-`media-breakpoint-down()` uses the breakpoint itself instead of the next breakpoint (e.g., `media-breakpoint-down(lg)` instead of `media-breakpoint-down(md)` targets viewports smaller than `lg`).
- Similarly, the second parameter in `media-breakpoint-between()` also uses the breakpoint itself instead of the next breakpoint (e.g., `media-between(sm, lg)` instead of `media-breakpoint-between(sm, md)` targets viewports between `sm` and `lg`).
-<spanclass="badge bg-danger">Breaking</span> Dropped `color()`, `theme-color()`, and `gray()` functions in favor of variables. [See #29083](https://github.com/twbs/bootstrap/pull/29083).
-<spanclass="badge bg-danger">Breaking</span> Renamed `theme-color-level()` function to `color-level()` and now accepts any color you want instead of only `$theme-color` colors. [See #29083](https://github.com/twbs/bootstrap/pull/29083) **Watch out:**`color-level()` was later on dropped in `v5.0.0-alpha3`.
-<spanclass="badge bg-danger">Breaking</span> Renamed `$enable-prefers-reduced-motion-media-query` and `$enable-pointer-cursor-for-buttons` to `$enable-reduced-motion` and `$enable-button-pointers` for brevity.
-<spanclass="badge bg-danger">Breaking</span> Removed the `bg-gradient-variant()` mixin. Use the `.bg-gradient` class to add gradients to elements instead of the generated `.bg-gradient-*` classes.
-<spanclass="badge bg-danger">Breaking</span> Renamed `scale-color()` function to `shift-color()` to avoid collision with Sass's own color scaling function.
- The color system which worked with `color-level()` and `$theme-color-interval` was removed in favor of a new color system. All `lighten()` and `darken()` functions in our codebase are replaced by `tint-color()` and `shade-color()`. These functions will mix the color with either white or black instead of changing its lightness by a fixed amount. The `shift-color()` will either tint or shade a color depending on whether its weight parameter is positive or negative. [See #30622](https://github.com/twbs/bootstrap/pull/30622) for more details.
- Improved color contrast. Bumped color contrast ratio from 3:1 to 4.5:1 and updated blue, green, cyan, and pink colors to ensure WCAG 2.1 AA contrast. Also changed our color contrast color from `$gray-900` to `$black`.
- **Improved gutters.** Gutters are now set in rems, and are narrower than v4 (`1.5rem`, or about `24px`, down from `30px`). This aligns our grid system's gutters with our spacing utilities.
- Added new [gutter class](https://getbootstrap.com/docs/5.1/layout/gutters/) (`.g-*`, `.gx-*`, and `.gy-*`) to control horizontal/vertical gutters, horizontal gutters, and vertical gutters.
-<spanclass="badge bg-danger">Breaking</span> Dropped several `.order-*` classes that often went unused. We now only provide `.order-1` to `.order-5` out of the box.
-<spanclass="badge bg-danger">Breaking</span> Dropped the `.media` component as it can be easily replicated with utilities. [See #28265](https://github.com/twbs/bootstrap/pull/28265) and the [flex utilities page for an example]({{< docsref "/utilities/flex#media-object" >}}).
-<spanclass="badge bg-danger">Breaking</span>`bootstrap-grid.css` now only applies `box-sizing: border-box` to the column instead of resetting the global box-sizing. This way, our grid styles can be used in more places without interference.
- **[RFS]({{<docsref"/getting-started/rfs">}}) is now enabled by default.** Headings using the `font-size()` mixin will automatically adjust their `font-size` to scale with the viewport. _This feature was previously opt-in with v4._
-<spanclass="badge bg-danger">Breaking</span> Overhauled our display typography to replace our `$display-*` variables and with a `$display-font-sizes` Sass map. Also removed the individual `$display-*-weight` variables for a single `$display-font-weight` and adjusted `font-size`s.
-<spanclass="badge bg-danger">Breaking</span>`.thead-light` and `.thead-dark` are dropped in favor of the `.table-*` variant classes which can be used for all table elements (`thead`, `tbody`, `tfoot`, `tr`, `th` and `td`).
-<spanclass="badge bg-danger">Breaking</span> The `table-row-variant()` mixin is renamed to `table-variant()` and accepts only 2 parameters: `$color` (color name) and `$value` (color code). The border color and accent colors are automatically calculated based on the table factor variables.
-<spanclass="badge bg-danger">Breaking</span>`.text-*` utilities do not add hover and focus states to links anymore. `.link-*` helper classes can be used instead. [See #29267](https://github.com/twbs/bootstrap/pull/29267)
-<spanclass="badge bg-danger">Breaking</span>`<hr>` elements now use `height` instead of `border` to better support the `size` attribute. This also enables use of padding utilities to create thicker dividers (e.g., `<hr class="py-1">`).
- Added `$enable-smooth-scroll`, which applies `scroll-behavior: smooth` globally—except for users asking for reduced motion through `prefers-reduced-motion` media query. [See #31877](https://github.com/twbs/bootstrap/pull/31877)
- Horizontal direction specific variables, utilities, and mixins have all been renamed to use logical properties like those found in flexbox layouts—e.g., `start` and `end` in lieu of `left` and `right`.
- **Added new floating forms!** We've promoted the Floating labels example to fully supported form components. [See the new Floating labels page.]({{< docsref "/forms/floating-labels" >}})
-<spanclass="badge bg-danger">Breaking</span>**Consolidated native and custom form elements.** Checkboxes, radios, selects, and other inputs that had native and custom classes in v4 have been consolidated. Now nearly all our form elements are entirely custom, most without the need for custom HTML.
-`.custom-check` is now `.form-check`.
-`.custom-check.custom-switch` is now `.form-check.form-switch`.
-`.custom-select` is now `.form-select`.
-`.custom-file` and `.form-file` have been replaced by custom styles on top of `.form-control`.
-`.custom-range` is now `.form-range`.
- Dropped native `.form-control-file` and `.form-control-range`.
-<spanclass="badge bg-danger">Breaking</span> Dropped `.input-group-append` and `.input-group-prepend`. You can now just add buttons and `.input-group-text` as direct children of the input groups.
- The longstanding [Missing border radius on input group with validation feedback bug](https://github.com/twbs/bootstrap/issues/25110) is finally fixed by adding an additional `.has-validation` class to input groups with validation.
-<spanclass="badge bg-danger">Breaking</span>**Dropped form-specific layout classes for our grid system.** Use our grid and utilities instead of `.form-group`, `.form-row`, or `.form-inline`.
-<spanclass="badge bg-danger">Breaking</span>`.form-text` no longer sets `display`, allowing you to create inline or block help text as you wish just by changing the HTML element.
- Unified `padding` values for alerts, breadcrumbs, cards, dropdowns, list groups, modals, popovers, and tooltips to be based on our `$spacer` variable. [See #30564](https://github.com/twbs/bootstrap/pull/30564).
-<spanclass="badge bg-danger">Breaking</span> Dropped all `.badge-*` color classes for background utilities (e.g., use `.bg-primary` instead of `.badge-primary`).
-<spanclass="badge bg-danger">Breaking</span>**[Toggle buttons](https://getbootstrap.com/docs/5.1/forms/checks-radios/#toggle-buttons), with checkboxes or radios, no longer require JavaScript and have new markup.** We no longer require a wrapping element, add `.btn-check` to the `<input>`, and pair it with any `.btn` classes on the `<label>`. [See #30650](https://github.com/twbs/bootstrap/pull/30650). _The docs for this has moved from our Buttons page to the new Forms section._
-<spanclass="badge bg-danger">Breaking</span>**Dropped `.btn-block` for utilities.** Instead of using `.btn-block` on the `.btn`, wrap your buttons with `.d-grid` and a `.gap-*` utility to space them as needed. Switch to responsive classes for even more control over them. [Read the docs for some examples.](https://getbootstrap.com/docs/5.1/components/buttons/#block-buttons)
-<spanclass="badge bg-danger">Breaking</span> Dropped `.card-deck` in favor of our grid. Wrap your cards in column classes and add a parent `.row-cols-*` container to recreate card decks (but with more control over responsive alignment).
-<spanclass="badge bg-danger">Breaking</span> Replaced the `.card` based accordion with a [new Accordion component]({{< docsref "/components/accordion" >}}).
- Added new [`.carousel-dark` variant]({{< docsref "/components/carousel#dark-variant" >}}) for dark text, controls, and indicators (great for lighter backgrounds).
- Close buttons now use a `background-image` (embedded SVG) instead of a `×` in the HTML, allowing for easier customization without the need to touch your markup.
-<spanclass="badge bg-danger">Breaking</span> All the events for the dropdown are now triggered on the dropdown toggle button and then bubbled up to the parent element.
- Dropdown menus now have a `data-bs-popper="static"` attribute set when the positioning of the dropdown is static and `data-bs-popper="none"` when dropdown is in the navbar. This is added by our JavaScript and helps us use custom position styles without interfering with Popper's positioning.
-<spanclass="badge bg-danger">Breaking</span> Dropped `flip` option for dropdown plugin in favor of native Popper configuration. You can now disable the flipping behavior by passing an empty array for [`fallbackPlacements`](https://popper.js.org/docs/v2/modifiers/flip/#fallbackplacements) option in [flip](https://popper.js.org/docs/v2/modifiers/flip/) modifier.
- Dropdown menus can now be clickable with a new `autoClose` option to handle the [auto close behavior]({{< docsref "/components/dropdowns#auto-close-behavior" >}}). You can use this option to accept the click inside or outside the dropdown menu to make it interactive.
-<spanclass="badge bg-danger">Breaking</span> Dropped the jumbotron component as it can be replicated with utilities. [See our new Jumbotron example for a demo.](https://getbootstrap.com/docs/5.1/examples/jumbotron/)
- Toasts can now be [positioned]({{< docsref "/components/toasts#placement" >}}) in a `.toast-container` with the help of [positioning utilities]({{< docsref "/utilities/position" >}}).
-<spanclass="badge bg-danger">Breaking</span> The default value for the `fallbackPlacements` is changed to `['top', 'right', 'bottom', 'left']` for better placement of popper elements.
-<spanclass="badge bg-danger">Breaking</span> Renamed several utilities to use logical property names instead of directional names with the addition of RTL support:
- Added new [position utilities]({{< docsref "/utilities/position#arrange-elements" >}}) for `top`, `right`, `bottom`, and `left`. Values include `0`, `50%`, and `100%` for each property.
- Added `.fs-*` utilities for `font-size` utilities (with RFS enabled). These use the same scale as HTML's default headings (1-6, large to small), and can be modified via Sass map.
-<spanclass="badge bg-danger">Breaking</span> Removed `.rounded-sm` and `rounded-lg`, and introduced a new scale of classes, `.rounded-0` to `.rounded-3`. [See #31687](https://github.com/twbs/bootstrap/pull/31687).
-<spanclass="badge bg-danger">Breaking</span>**Responsive embed helpers have been renamed to [ratio helpers]({{< docsref "/helpers/ratio" >}})** with new class names and improved behaviors, as well as a helpful CSS variable.
- Classes have been renamed to change `by` to `x` in the aspect ratio. For example, `.ratio-16by9` is now `.ratio-16x9`.
- We've dropped the `.embed-responsive-item` and element group selector in favor of a simpler `.ratio > *` selector. No more class is needed, and the ratio helper now works with any HTML element.
- The `$embed-responsive-aspect-ratios` Sass map has been renamed to `$aspect-ratios` and its values have been simplified to include the class name and the percentage as the `key: value` pair.
- CSS variables are now generated and included for each value in the Sass map. Modify the `--bs-aspect-ratio` variable on the `.ratio` to create any [custom aspect ratio]({{< docsref "/helpers/ratio#custom-ratios" >}}).
-<spanclass="badge bg-danger">Breaking</span> Data attributes for all JavaScript plugins are now namespaced to help distinguish Bootstrap functionality from third parties and your own code. For example, we use `data-bs-toggle` instead of `data-toggle`.
- **All plugins can now accept a CSS selector as the first argument.** You can either pass a DOM element or any valid CSS selector to create a new instance of the plugin:
```js
var modal = new bootstrap.Modal('#myModal')
var dropdown = new bootstrap.Dropdown('[data-bs-toggle="dropdown"]')
```
-`popperConfig` can be passed as a function that accepts the Bootstrap's default Popper config as an argument, so that you can merge this default configuration in your way. **Applies to dropdowns, popovers, and tooltips.**
- The default value for the `fallbackPlacements` is changed to `['top', 'right', 'bottom', 'left']` for better placement of Popper elements. **Applies to dropdowns, popovers, and tooltips.**
- Removed underscore from public static methods like `_getInstance()` → `getInstance()`.
