---
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.
