--- 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/4.6/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 `<table>` 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. ## Page defaults The `<html>` and `<body>` 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 `<html>`, but `16px` is assumed (the browser default). `font-size: 1rem` is applied on the `<body>` for easy responsive type-scaling via media queries while respecting user preferences and ensuring a more accessible approach. - The `<body>` also sets a global `font-family`, `line-height`, and `text-align`. This is inherited later by some form elements to prevent font inconsistencies. - For safety, the `<body>` has a declared `background-color`, defaulting to `#fff`. ## Native font stack The default web fonts (Helvetica Neue, Helvetica, and Arial) have been dropped in Bootstrap 4 and replaced with a "native font stack" for optimum text rendering on every device and OS. Read more about [native font stacks in this *Smashing Magazine* article](https://www.smashingmagazine.com/2015/11/using-system-ui-fonts-practical-guide/). ```scss $font-family-sans-serif: // Safari for macOS and iOS (San Francisco) -apple-system, // Chrome < 56 for macOS (San Francisco) BlinkMacSystemFont, // Windows "Segoe UI", // Android Roboto, // Basic web fallback "Helvetica Neue", Arial, // Linux "Noto Sans", "Liberation Sans", // Sans serif fallback sans-serif, // Emoji fonts "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji" !default; ``` Note that because the font stack includes emoji fonts, many common symbol/dingbat unicode characters will be rendered as multi-colored pictographs. Their appearance will vary, depending on the style used in the browser/platform's native emoji font, and they won't be affected by any CSS `color` styles. This `font-family` is applied to the `<body>` and automatically inherited globally throughout Bootstrap. To switch the global `font-family`, update `$font-family-base` and recompile Bootstrap. ## Headings and paragraphs All heading elements—e.g., `<h1>`—and `<p>` are reset to have their `margin-top` removed. Headings have `margin-bottom: .5rem` added and paragraphs `margin-bottom: 1rem` for easy spacing. <table> <thead> <tr> <th>Heading</th> <th>Example</th> </tr> </thead> <tbody> <tr> <td> {{< markdown >}}`<h1></h1>`{{< /markdown >}} </td> <td><span class="h1">h1. Bootstrap heading</span></td> </tr> <tr> <td> {{< markdown >}}`<h2></h2>`{{< /markdown >}} </td> <td><span class="h2">h2. Bootstrap heading</span></td> </tr> <tr> <td> {{< markdown >}}`<h3></h3>`{{< /markdown >}} </td> <td><span class="h3">h3. Bootstrap heading</span></td> </tr> <tr> <td> {{< markdown >}}`<h4></h4>`{{< /markdown >}} </td> <td><span class="h4">h4. Bootstrap heading</span></td> </tr> <tr> <td> {{< markdown >}}`<h5></h5>`{{< /markdown >}} </td> <td><span class="h5">h5. Bootstrap heading</span></td> </tr> <tr> <td> {{< markdown >}}`<h6></h6>`{{< /markdown >}} </td> <td><span class="h6">h6. Bootstrap heading</span></td> </tr> </tbody> </table> ## Lists All lists—`<ul>`, `<ol>`, and `<dl>`—have their `margin-top` removed and a `margin-bottom: 1rem`. Nested lists have no `margin-bottom`. <div class="bd-example"> {{< markdown >}} * All lists have their top margin removed * And their bottom margin normalized * Nested lists have no bottom margin * This way they have a more even appearance * Particularly when followed by more list items * The left padding has also been reset 1. Here's an ordered list 2. With a few list items 3. It has the same overall look 4. As the previous unordered list {{< /markdown >}} </div> For simpler styling, clear hierarchy, and better spacing, description lists have updated `margin`s. `<dd>`s reset `margin-left` to `0` and add `margin-bottom: .5rem`. `<dt>`s are **bolded**. <div class="bd-example"> <dl> <dt>Description lists</dt> <dd>A description list is perfect for defining terms.</dd> <dt>Term</dt> <dd>Definition for the term.</dd> <dd>A second definition for the same term.</dd> <dt>Another term</dt> <dd>Definition for this other term.</dd> </dl> </div> ## Preformatted text The `<pre>` element is reset to remove its `margin-top` and use `rem` units for its `margin-bottom`. <div class="bd-example"> <pre> .example-element { margin-bottom: 1rem; } </pre> </div> ## Tables Tables are slightly adjusted to style `<caption>`s, collapse borders, and ensure consistent `text-align` throughout. Additional changes for borders, padding, and more come with [the `.table` class]({{< docsref "/content/tables" >}}). <div class="bd-example"> <table> <caption> This is an example table, and this is its caption to describe the contents. </caption> <thead> <tr> <th>Table heading</th> <th>Table heading</th> <th>Table heading</th> <th>Table heading</th> </tr> </thead> <tbody> <tr> <td>Table cell</td> <td>Table cell</td> <td>Table cell</td> <td>Table cell</td> </tr> <tr> <td>Table cell</td> <td>Table cell</td> <td>Table cell</td> <td>Table cell</td> </tr> <tr> <td>Table cell</td> <td>Table cell</td> <td>Table cell</td> <td>Table cell</td> </tr> </tbody> </table> </div> ## Forms Various form elements have been rebooted for simpler base styles. Here are some of the most notable changes: - `<fieldset>`s have no borders, padding, or margin so they can be easily used as wrappers for individual inputs or groups of inputs. - `<legend>`s, like fieldsets, have also been restyled to be displayed as a heading of sorts. - `<label>`s are set to `display: inline-block` to allow `margin` to be applied. - `<input>`s, `<select>`s, `<textarea>`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="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"></textarea> </p> <p> <label for="date">Example date</label> <input type="date" id="date"> </p> <p> <label for="time">Example time</label> <input type="time" id="time"> </p> <p> <label for="output">Example output</label> <output name="result" id="output">100</output> </p> <p> <button type="submit">Button submit</button> <input type="submit" value="Input submit button"> <input type="reset" value="Input reset button"> <input type="button" value="Input button"> </p> <p> <button type="submit" disabled>Button submit</button> <input type="submit" value="Input submit button" disabled> <input type="reset" value="Input reset button" disabled> <input type="button" value="Input button" disabled> </p> </fieldset> </form> ### 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 `<button>` elements, which get their own `cursor` change. {{< example >}} <span role="button" tabindex="0">Non-button element button</span> {{< /example >}} ## Misc elements ### Address The `<address>` element is updated to reset the browser default `font-style` from `italic` to `normal`. `line-height` is also now inherited, and `margin-bottom: 1rem` has been added. `<address>`s are for presenting contact information for the nearest ancestor (or an entire body of work). Preserve formatting by ending lines with `<br>`. <div class="bd-example"> <address> <strong>Twitter, Inc.</strong><br> 1355 Market St, Suite 900<br> San Francisco, CA 94103<br> <abbr title="Phone">P:</abbr> (123) 456-7890 </address> <address> <strong>Full Name</strong><br> <a href="mailto:first.last@example.com">first.last@example.com</a> </address> </div> ### Blockquote The default `margin` on blockquotes is `1em 40px`, so we reset that to `0 0 1rem` for something more consistent with other elements. <div class="bd-example"> <blockquote class="blockquote"> <p>A well-known quote, contained in a blockquote element.</p> <footer>Someone famous in <cite title="Source Title">Source Title</cite></footer> </blockquote> </div> ### Inline elements The `<abbr>` element receives basic styling to make it stand out amongst paragraph text. <div class="bd-example"> Nulla <abbr title="attribute">attr</abbr> vitae elit libero, a pharetra augue. </div> ### Summary The default `cursor` on summary is `text`, so we reset that to `pointer` to convey that the element can be interacted with by clicking on it. <div class="bd-example"> <details> <summary>Some details</summary> <p>More info about the details.</p> </details> <details open> <summary>Even more details</summary> <p>Here are even more details about the details.</p> </details> </div> ## HTML5 `[hidden]` attribute HTML5 adds [a new global attribute named `[hidden]`](https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/hidden), which is styled as `display: none` by default. Borrowing an idea from [PureCSS](https://purecss.io/), we improve upon this default by making `[hidden] { display: none !important; }` to help prevent its `display` from getting accidentally overridden. While `[hidden]` isn't natively supported by IE10, the explicit declaration in our CSS gets around that problem. ```html <input type="text" hidden> ``` {{< callout warning >}} ##### jQuery incompatibility `[hidden]` is not compatible with jQuery's `$(...).hide()` and `$(...).show()` methods. Therefore, we don't currently especially endorse `[hidden]` over other techniques for managing the `display` of elements. {{< /callout >}} To merely toggle the visibility of an element, meaning its `display` is not modified and the element can still affect the flow of the document, use [the `.invisible` class]({{< docsref "/utilities/visibility" >}}) instead.
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