--- layout: docs title: Reboot description: Reboot, a collection of element-specific CSS changes in a single file, kickstart Bootstrap to provide an elegant, consistent, and simple baseline to build upon. group: content aliases: "/docs/5.1/content/" toc: true --- ## Approach Reboot builds upon Normalize, providing many HTML elements with somewhat opinionated styles using only element selectors. Additional styling is done only with classes. For example, we reboot some `` styles for a simpler baseline and later provide `.table`, `.table-bordered`, and more. Here are our guidelines and reasons for choosing what to override in Reboot: - Update some browser default values to use `rem`s instead of `em`s for scalable component spacing. - Avoid `margin-top`. Vertical margins can collapse, yielding unexpected results. More importantly though, a single direction of `margin` is a simpler mental model. - For easier scaling across device sizes, block elements should use `rem`s for `margin`s. - Keep declarations of `font`-related properties to a minimum, using `inherit` whenever possible. ## CSS variables Added in v5.1.1 With v5.1.1, we standardized our required `@import`s across all our CSS bundles (including `bootstrap.css`, `bootstrap-reboot.css`, and `bootstrap-grid.css` to include `_root.scss` . This adds `:root` level CSS variables to all bundles, regardless of how many of them are used in that bundle. Ultimately Bootstrap 5 will continue to see more CSS variables added over time. ## Page defaults The `` and `` elements are updated to provide better page-wide defaults. More specifically: - The `box-sizing` is globally set on every element—including `*::before` and `*::after`, to `border-box`. This ensures that the declared width of element is never exceeded due to padding or border. - No base `font-size` is declared on the ``, but `16px` is assumed (the browser default). `font-size: 1rem` is applied on the `` for easy responsive type-scaling via media queries while respecting user preferences and ensuring a more accessible approach. This browser default can be overridden by modifying the `$font-size-root` variable. - The `` also sets a global `font-family`, `font-weight`, `line-height`, and `color`. This is inherited later by some form elements to prevent font inconsistencies. - For safety, the `` has a declared `background-color`, defaulting to `#fff`. ## Native font stack Bootstrap utilizes a "native font stack" or "system font stack" for optimum text rendering on every device and OS. These system fonts have been designed specifically with today's devices in mind, with improved rendering on screens, variable font support, and more. Read more about [native font stacks in this *Smashing Magazine* article](https://www.smashingmagazine.com/2015/11/using-system-ui-fonts-practical-guide/). ```scss $font-family-sans-serif: // Cross-platform generic font family (default user interface font) system-ui, // Safari for macOS and iOS (San Francisco) -apple-system, // Windows "Segoe UI", // Android Roboto, // Basic web fallback "Helvetica Neue", Arial, // Linux "Noto Sans", "Liberation Sans", // Sans serif fallback sans-serif, // Emoji fonts "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji" !default; ``` Note that because the font stack includes emoji fonts, many common symbol/dingbat unicode characters will be rendered as multi-colored pictographs. Their appearance will vary, depending on the style used in the browser/platform's native emoji font, and they won't be affected by any CSS `color` styles. This `font-family` is applied to the `` and automatically inherited globally throughout Bootstrap. To switch the global `font-family`, update `$font-family-base` and recompile Bootstrap. ## CSS variables As Bootstrap 5 continues to mature, more and more styles will be built with [CSS variables]({{< docsref "/customize/css-variables" >}}) as a means to provide more real-time customization without the need to always recompile Sass. Our approach is to take our source Sass variables and transform them into CSS variables. That way, even if you don't use CSS variables, you still have all the power of Sass. **This is still in-progress and will take time to fully implement.** For example, consider these `:root` CSS variables for common `` styles: {{< scss-docs name="root-body-variables" file="scss/_root.scss" >}} In practice, those variables are then applied in Reboot like so: {{< scss-docs name="reboot-body-rules" file="scss/_reboot.scss" >}} Which allows you to make real-time customizations however you like: ```html ``` ## Headings and paragraphs All heading elements—e.g., `

`—and `
` are reset to have their `margin-top` removed. Headings have `margin-bottom: .5rem` added and paragraphs `margin-bottom: 1rem` for easy spacing.

Heading	Example
{{< markdown >}}` `{{< /markdown >}}	h1. Bootstrap heading
{{< markdown >}}` `{{< /markdown >}}	h2. Bootstrap heading
{{< markdown >}}` `{{< /markdown >}}	h3. Bootstrap heading
{{< markdown >}}` `{{< /markdown >}}	h4. Bootstrap heading
{{< markdown >}}` `{{< /markdown >}}	h5. Bootstrap heading
{{< markdown >}}` `{{< /markdown >}}	h6. Bootstrap heading

## Lists All lists—`

`s reset `margin-left` to `0` and add `margin-bottom: .5rem`. `
`s are **bolded**.

Description lists

A description list is perfect for defining terms.

Term

Definition for the term.

A second definition for the same term.

Another term

Definition for this other term.

## Inline code Wrap inline snippets of code with ``. Be sure to escape HTML angle brackets. {{< example >}} For example, <section> should be wrapped as inline. {{< /example >}} ## Code blocks Use ``s for multiple lines of code. Once again, be sure to escape any angle brackets in the code for proper rendering. The `` element is reset to remove its `margin-top` and use `rem` units for its `margin-bottom`. {{< example >}} <p>Sample text here...</p> <p>And another line of sample text here...</p> {{< /example >}} ## Variables For indicating variables use the `` tag. {{< example >}} y = mx + b {{< /example >}} ## User input Use the `` to indicate input that is typically entered via keyboard. {{< example >}} To switch directories, type cd followed by the name of the directory. To edit settings, press ctrl + , {{< /example >}} ## Sample output For indicating sample output from a program use the `` tag. {{< example >}} This text is meant to be treated as sample output from a computer program. {{< /example >}} ## Tables Tables are slightly adjusted to style ``s, collapse borders, and ensure consistent `text-align` throughout. Additional changes for borders, padding, and more come with [the `.table` class]({{< docsref "/content/tables" >}}). This is an example table, and this is its caption to describe the contents. Table heading Table heading Table heading Table heading Table cell Table cell Table cell Table cell Table cell Table cell Table cell Table cell Table cell Table cell Table cell Table cell ## Forms Various form elements have been rebooted for simpler base styles. Here are some of the most notable changes: - ``s have no borders, padding, or margin so they can be easily used as wrappers for individual inputs or groups of inputs. - ``s, like fieldsets, have also been restyled to be displayed as a heading of sorts. - ``s are set to `display: inline-block` to allow `margin` to be applied. - ``s, ``s, and `<button>`s are mostly addressed by Normalize, but Reboot removes their `margin` and sets `line-height: inherit`, too. - `<textarea>`s are modified to only be resizable vertically as horizontal resizing often "breaks" page layout. - `<button>`s and `<input>` button elements have `cursor: pointer` when `:not(:disabled)`. These changes, and more, are demonstrated below. <form class="bd-example"> <fieldset> <legend>Example legend</legend> <p> <label for="input">Example input</label> <input type="text" id="input" placeholder="Example input"> </p> <p> <label for="email">Example email</label> <input type="email" id="email" placeholder="test@example.com"> </p> <p> <label for="tel">Example telephone</label> <input type="tel" id="tel"> </p> <p> <label for="url">Example url</label> <input type="url" id="url"> </p> <p> <label for="number">Example number</label> <input type="number" id="number"> </p> <p> <label for="search">Example search</label> <input type="search" id="search"> </p> <p> <label for="range">Example range</label> <input type="range" id="range" min="0" max="10"> </p> <p> <label for="file">Example file input</label> <input type="file" id="file"> </p> <p> <label for="select">Example select</label> <select id="select"> <option value="">Choose...</option> <optgroup label="Option group 1"> <option value="">Option 1</option> <option value="">Option 2</option> <option value="">Option 3</option> </optgroup> <optgroup label="Option group 2"> <option value="">Option 4</option> <option value="">Option 5</option> <option value="">Option 6</option> </optgroup> </select> </p> <p> <label> <input type="checkbox" value=""> Check this checkbox </label> </p> <p> <label> <input type="radio" name="optionsRadios" id="optionsRadios1" value="option1" checked> Option one is this and that </label> <label> <input type="radio" name="optionsRadios" id="optionsRadios2" value="option2"> Option two is something else that's also super long to demonstrate the wrapping of these fancy form controls. </label> <label> <input type="radio" name="optionsRadios" id="optionsRadios3" value="option3" disabled> Option three is disabled </label> </p> <p> <label for="textarea">Example textarea</label> <textarea id="textarea" rows="3"> Example date Example time Example password Example datetime-local Example week Example month Example color Example output 100 {{< callout warning >}} {{< partial "callout-warning-input-support.md" >}} {{< /callout >}} ### Pointers on buttons Reboot includes an enhancement for `role="button"` to change the default cursor to `pointer`. Add this attribute to elements to help indicate elements are interactive. This role isn't necessary for `

Table heading	Table heading	Table heading	Table heading
Table cell	Table cell	Table cell	Table cell
Table cell	Table cell	Table cell	Table cell
Table cell	Table cell	Table cell	Table cell

`—and `` are reset to have their `margin-top` removed. Headings have `margin-bottom: .5rem` added and paragraphs `margin-bottom: 1rem` for easy spacing.

`—and `
` are reset to have their `margin-top` removed. Headings have `margin-bottom: .5rem` added and paragraphs `margin-bottom: 1rem` for easy spacing.