- Extended form validation states customization capabilities. Added three new optional parameters to the `form-validation-state` mixin: `tooltip-color`, `tooltip-bg-color`, `focus-box-shadow`. These parameters can be set in the `$form-validation-states` map. [See #31757](https://github.com/twbs/bootstrap/pull/31757).
- Dropdown menus now have a `data-bs-popper="static"` attribute set when the positioning of the dropdown is static and `data-bs-popper="none"` when dropdown is in the navbar. This is added by our JavaScript and helps us use custom position styles without interfering with Popper's positioning.
-`popperConfig` can be passed as a function that accepts the Bootstrap's default Popper config as an argument, so that you can merge this default configuration in your way.
**The RTL feature is still experimental and will probably evolve according to user feedback.** Spotted something or have an improvement to suggest? [Open an issue]({{< param repo >}}/issues/new), we'd love to get your insights.
#### Sass
Horizontal direction sensitive variables, utilities and mixins are renamed with more logical names — `start` and `end` in lieu of `left` and `right`.
- Renamed `border-left-radius()` and `border-right-radius()` to `border-start-radius()` and `border-end-radius()` — as well as their corner relative variants (eg. `.border-bottom-left-radius` became `.border-bottom-start-radius`).
- Renamed `caret-left()` and `caret-right()` to `caret-start()` and `caret-end()` — subsequently, the `caret()` mixin now takes `start` and `end` as arguments instead of `left` and `right`.
##### Variables
- New `$breadcrumb-divider-flipped` if a different breadcrumb separator is needed in RTL.
- Renamed `$navbar-brand-margin-right` to `$navbar-brand-margin-end`.
- Renamed `$pagination-margin-left` to `$pagination-margin-start`.
- Renamed `$form-check-padding-left` to `$form-check-padding-start`.
- Renamed `$form-switch-padding-left` to `$form-switch-padding-start`.
- Renamed `$form-check-inline-margin-right` to `$form-check-inline-margin-end`.
- Renamed `$form-select-feedback-icon-padding-right` to `$form-select-feedback-icon-padding-end`.
- 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`.
- Toasts can now be [positioned]({{< docsref "/components/toasts#placement" >}}) in a `.toast-container` with the help of [positioning utilities]({{< docsref "/utilities/position" >}}).
- The color system which worked with `color-level()` and `$theme-color-interval` was removed in favor of a new color system. All `lighten()` and `darken()` functions in our codebase are replaced by `tint-color()` and `shade-color()`. These functions will mix the color with either white or black instead of changing its lightness by a fixed amount. The `scale-color()` (changed to `shift-color()` in Beta 1) will either tint or shade a color depending on whether its weight parameter is positive or negative. [See #30622](https://github.com/twbs/bootstrap/pull/30622) for more details.
- Introduce `$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)
- [Dropped `.btn-block` in favor of CSS grid utility classes.]({{< docsref "/components/buttons#block-buttons" >}}) Instead of applying `.btn-block` to individual buttons, a group of buttons now get wrapped in a parent `.d-grid` class and can use `.gap-*` utilities for spacing. For individual "block buttons", add `.w-100`.
- 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.
- Promoted the Floating labels example to fully supported form component. [See the new Floating labels page.]({{< docsref "/forms/floating-labels" >}})
- File inputs now use the `.form-control` class and don't require JavaScript, additional HTML, or additional classes. [See #31955](https://github.com/twbs/bootstrap/pull/31955).
- 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.
- Renamed `.font-weight-*` utilities as `.fw-*` for brevity and consistency.
- Renamed `.font-style-*` utilities as `.fst-*` for brevity and consistency.
- [#31383](https://github.com/twbs/bootstrap/pull/31383): Resized checks and radios to be `1em` instead of `1.25em` in an effort to make them scale better with custom `$font-size-base` values and more.
- [#30639](https://github.com/twbs/bootstrap/pull/30639): Disabled states of buttons are easier to customize thanks to additional arguments in the `button-variant()` mixin.
- Replaced chevron icons for carousel controls with new SVGs from [Bootstrap Icons]({{< param "icons" >}}).
- Added new [`.carousel-dark` variant]({{< docsref "/components/carousel#dark-variant" >}}) for dark text, controls, and indicators (great for lighter backgrounds).
- Renamed `.close` to `.btn-close` for a less generic name.
- Close buttons now use a `background-image` (embedded SVG) instead of a `×` in the HTML, allowing for easier customization without the need to touch your markup.
- Added new variables to better control the customization.
- [#31035](https://github.com/twbs/bootstrap/pull/31035): Added new `null` variables for `font-size`, `font-weight`, `color`, and `:hover``color` to the `.nav-link` class.
- [#31109](https://github.com/twbs/bootstrap/pull/31109): Made default toast duration 5 seconds.
- [#31155](https://github.com/twbs/bootstrap/pull/31155): Clear `timeout` before showing toasts.
- [#31381](https://github.com/twbs/bootstrap/pull/31381): Removed `overflow: hidden` from toasts and replaced with proper `border-radius`s with `calc()` functions.
- Responsive embed helpers have been renamed to [ratio helpers]({{< docsref "/helpers/ratio" >}}) with new class names and improved behaviors, as well as a helpful CSS variable.
- Classes have been renamed to change `by` to `x` in the aspect ratio. For example, `.ratio-16by9` is now `.ratio-16x9`.
- We've dropped the `.embed-responsive-item` and element group selector in favor of a simpler `.ratio > *` selector. No more class is needed, and the ratio helper now works with any HTML element.
- The `$embed-responsive-aspect-ratios` Sass map has been renamed to `$aspect-ratios` and its values have been simplified to include the class name and the percentage as the `key: value` pair.
- CSS variables are now generated and included for each value in the Sass map. Modify the `--aspect-ratio` variable on the `.ratio` to create any [custom aspect ratio]({{< docsref "/helpers/ratio#custom-ratios" >}}).
- [#31280](https://github.com/twbs/bootstrap/pull/31280): Added new [position utilities]({{< docsref "/utilities/position#arrange-elements" >}}) for `top`, `right`, `bottom`, and `left`. Values include `0`, `50%`, and `100%` for each property.
- [#31484](https://github.com/twbs/bootstrap/pull/31484): Added new [`border-width` utility]({{< docsref "/utilities/borders#border-width" >}}).
- [#31473](https://github.com/twbs/bootstrap/pull/31473): The `.d-none` utility was moved in our CSS to give it more weight over other display utilities.
- Removed `hover`, `hover-focus`, `plain-hover-focus`, and `hover-focus-active` mixins. Use regular CSS syntax for these moving forward. [See #28267](https://github.com/twbs/bootstrap/pull/28267).
- Removed print styles and `$enable-print-styles` variable. Print display classes, however, have remained intact. [See #28339](https://github.com/twbs/bootstrap/pull/28339).
- The `theme-color-level()` function is renamed to `color-level()` and now accepts any color you want instead of only `$theme-color` colors. [See #29083](https://github.com/twbs/bootstrap/pull/29083) **Watch out:**`color-level()` was later on dropped in `v5.0.0-alpha3`.
- Renamed `$enable-prefers-reduced-motion-media-query` and `$enable-pointer-cursor-for-buttons` to `$enable-reduced-motion` and `$enable-button-pointers` for brevity.
- Line heights are dropped from several components to simplify our codebase. The `button-size()` and `pagination-size()` do not accept line height parameters anymore. [See #29271](https://github.com/twbs/bootstrap/pull/29271)
- The `button-variant()` mixin now accepts 3 optional color parameters, for each button state, to override the color provided by `color-contrast()`. By default, these parameters will find which color provides more contrast against the button state's background color with `color-contrast()`.
- The `button-outline-variant()` mixin now accepts an additional argument, `$active-color`, for setting the button's active state text color. By default, this parameter will find which color provides more contrast against the button's active background color with `color-contrast()`.
- Ditch the Sass map merges, which makes it easier to remove redundant values. Keep in mind you now have to define all values in the Sass maps like `$theme-colors`. Check out how to deal with [Sass maps]({{< docsref "/customize/sass#maps-and-loops" >}}).
-`color-yiq()` function and related variables are renamed to `color-contrast()` since it's not related to YIQ colorspace anymore. [See #30168.](https://github.com/twbs/bootstrap/pull/30168/)
- The `bg-gradient-variant()` mixin is removed since the `.bg-gradient` class can now be used to add gradients to elements instead of the `.bg-gradient-*` classes.
- The `media-breakpoint-down()` uses the breakpoint itself instead of the next breakpoint. Use `media-breakpoint-down(lg)` instead of `media-breakpoint-down(md)` to target viewports smaller than the `lg` breakpoint.
- The `media-breakpoint-between()` mixin's second parameter also uses the breakpoint itself instead of the next breakpoint. Use `media-between(sm, lg)` instead of `media-breakpoint-between(sm, md)` to target viewports between the `sm` and `lg` breakpoints.
- The `box-shadow()` mixin now better supports `none` and `null` with multiple arguments. Now you can pass multiple arguments with either value and get the expected output. [See #30394](https://github.com/twbs/bootstrap/pull/30394).
- Each `border-radius()` mixin now has a default value. You can now call these mixins without specifying a border radius value and the `$border-radius` variable will be used. [See #31571](https://github.com/twbs/bootstrap/pull/31571)
-`bootstrap-grid.css` now only applies `box-sizing: border-box` to the column instead of resetting the global box-sizing. This way the grid system can be used, even if `box-sizing: border-box` is not applied to each element.
- Simplified table styles (no more odd top border) and tightened cell padding.
- Nested tables do not inherit styles anymore.
-`.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`).
- The `table-row-variant()` mixin is renamed to `table-variant()` and accepts only 2 parameters: `$color` (colon name) and `$value` (color code). The border color and accent colors are automatically calculated based on the table factor variables.
-`.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)
- Renamed `.custom-file` to `.form-file` (including variables). **Watch out:**`.form-file` was later on dropped in `v5.0.0-alpha3`, now you can use `.form-control`.
- 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.
- Form labels now require the `.form-label` class. Sass variables are now available to style form labels to your needs. [See #30476](https://github.com/twbs/bootstrap/pull/30476)
-`.form-text` no longer sets `display`, but does set `color` and `font-size`. So instead of `<small class="form-text text-muted">` you should now use `<div class="form-text">`.
- Unified `padding` values for alerts, breadcrumbs, cards, dropdowns, list groups, modals, popovers, and tooltips to be based on our `$spacer` variable. [See #30564](https://github.com/twbs/bootstrap/pull/30564).
- Disabled states of the buttons, close button, pagination link & form range now have `pointer-events: none` added. This simplifies our codebase and makes it easier to override active states in CSS. [#29296](https://github.com/twbs/bootstrap/pull/29296).
- Removed auto-darkening of `<hr>` elements in `.alert-*` class variants. `<hr>`s use `rgba()` for their color, so these should naturally blend anyway.
- The checkbox/radio toggle is removed from the button plugin in favor of a CSS only solution, which is documented in the [form checks and radios]({{< docsref "/forms/checks-radios#toggle-buttons" >}}) docs. The `.btn-check` class can be added to inputs, any label with `.btn` and modifier class can be used to theme the labels. [See #30650](https://github.com/twbs/bootstrap/pull/30650).
- All navbars now require a container within. This drastically simplifies spacing requirements and removes the need for extensive CSS overrides we added for responsive containers in v4.
- Unlike the old `.sr-only-focusable`, which only worked in combination with `.sr-only`, `.sr-only-focusable` can be used as a standalone class without `.sr-only`. [See #28720](https://github.com/twbs/bootstrap/pull/28720).
- Decreased the number of responsive order utilities per breakpoint. The highest order utility with a number now is `.order-5` instead of `.order-12`. [See #28874](https://github.com/twbs/bootstrap/pull/28874).
- Negative margin utilities are disabled by default. You can re-enable them by setting `$enable-negative-margins: true`, but keep in mind this can increase the file size quite a lot.
