Source

Reboot

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.

On this page

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 rems instead of ems for scalable component spacing.
Avoid margin-top. Vertical margins can collapse, yielding unexpected results. More importantly though, a single direction of marginis a simpler mental model.
For easier scaling across device sizes, block elements should use rems for margins.
Keep declarations of font-related properties to a minimum, using inheritwhenever possible.

CSS variables

Added in v5.2.0

With v5.1.1, we standardized our required @imports across all our CSS bundles (including bootstrap.css, bootstrap-reboot.css, and bootstrap-grid.css) to include _root.scss. This adds :rootlevel 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, in order 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 :rootCSS variables for common <body>styles:

  @if $font-size-root != null {
    --#{$prefix}root-font-size: #{$font-size-root};
  }
  --#{$prefix}body-font-family: #{$font-family-base};
  @include rfs($font-size-base, --#{$prefix}body-font-size);
  --#{$prefix}body-font-weight: #{$font-weight-base};
  --#{$prefix}body-line-height: #{$line-height-base};
  --#{$prefix}body-color: #{$body-color};
  @if $body-text-align != null {
    --#{$prefix}body-text-align: #{$body-text-align};
  }
  --#{$prefix}body-bg: #{$body-bg};

In practice, those variables are then applied in Reboot like so:

body {
  margin: 0; // 1
  font-family: var(--#{$prefix}body-font-family);
  @include font-size(var(--#{$prefix}body-font-size));
  font-weight: var(--#{$prefix}body-font-weight);
  line-height: var(--#{$prefix}body-line-height);
  color: var(--#{$prefix}body-color);
  text-align: var(--#{$prefix}body-text-align);
  background-color: var(--#{$prefix}body-bg); // 2
  -webkit-text-size-adjust: 100%; // 3
  -webkit-tap-highlight-color: rgba($black, 0); // 4
}

Which allows you to make real-time customizations however you like:

<body style="--bs-body-color: #333;">
  <!-- ... -->
</body>

Page defaults

The <html>and <body>elements are updated to provide better page-wide defaults. More specifically:

The box-sizingis globally set on every element—including *::beforeand *::after, to border-box. This ensures that the declared width of element is never exceeded due to padding or border.
- No base font-sizeis declared on the <html>, but 16pxis assumed (the browser default). font-size: 1remis applied on the <body>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-rootvariable.
The <body>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 <body>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 .

$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,
  // older macOS and iOS
  "Helvetica Neue"
  // Linux
  "Noto Sans",
  "Liberation Sans",
  // Basic web fallback
  Arial,
  // 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 multicolored 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 colorstyles.

This font-familyis applied to the <body>and automatically inherited globally throughout Bootstrap. To switch the global font-family, update $font-family-baseand recompile Bootstrap.

Headings and paragraphs

All heading elements—eg, <h1>—and <p>are reset to have their margin-topremoved. Headings have margin-bottom: .5remadded and paragraphs margin-bottom: 1remfor easy spacing.

heading	example
`<h1></h1>`	h1. Bootstrap heading
`<h2></h2>`	h2. Bootstrap heading
`<h3></h3>`	h3. Bootstrap heading
`<h4></h4>`	h4. Bootstrap heading
`<h5></h5>`	h5. Bootstrap heading
`<h6></h6>`	h6. Bootstrap heading

horizontal rules

The <hr>element has been simplified. Similar to browser defaults, <hr>s are styled via border-top, have a default opacity: .25, and automatically inherit their border-colorvia color, including when coloris set via the parent. They can be modified with text, border, and opacity utilities.

html

<hr>

<div class="text-success">
  <hr>
</div>

<hr class="border border-danger border-2 opacity-50">
<hr class="border border-primary border-3 opacity-75">

Lists

All lists— <ul>, <ol>, and <dl>—have their margin-topremoved and a margin-bottom: 1rem. Nested lists have no margin-bottom. We've also reset the padding-lefton <ul>and <ol>elements.

All lists have their top margins 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

Here's an ordered list
With a few list items
It has the same overall look
As the previous unordered list

For simpler styling, clear hierarchy, and better spacing, description lists have updated margins. <dd>s reset margin-leftto 0and add margin-bottom: .5rem. <dt>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 <code>. Be sure to escape HTML angle brackets.

For example, <section>should be wrapped as inline.

html

For example, <code>&lt;section&gt;</code> should be wrapped as inline.

code blocks

Use <pre>s for multiple lines of code. Once again, be sure to escape any angle brackets in the code for proper rendering. The <pre>element is reset to remove its margin-topand use remunits for its margin-bottom.

<p>Sample text here...</p>
<p>And another line of sample text here...</p>

html

<pre><code>&lt;p&gt;Sample text here...&lt;/p&gt;
&lt;p&gt;And another line of sample text here...&lt;/p&gt;
</code></pre>

Variables

For indicating variables use the <var>tag.

y = m x + b

html

<var>y</var> = <var>m</var><var>x</var> + <var>b</var>

user input

Use the <kbd>to indicate input that is typically entered via keyboard.

To switch directories, type cdfollowed by the name of the directory.
To edit settings, press ctrl + ,

html

To switch directories, type <kbd>cd</kbd> followed by the name of the directory.<br>
To edit settings, press <kbd><kbd>ctrl</kbd> + <kbd>,</kbd></kbd>

sample output

For indicating sample output from a program use the <samp>tag.

This text is meant to be treated as sample output from a computer program.

html

<samp>This text is meant to be treated as sample output from a computer program.</samp>

tables

Tables are slightly adjusted to style <caption>s, collapse borders, and ensure consistent text-alignthroughout. Additional changes for borders, padding, and more come with the .tableclass .

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

html

<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>

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-blockallow marginto be applied.
<input>s, <select>s, <textarea>s, and <button>s are mostly addressed by Normalize, but Reboot removes their marginand 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: pointerwhen :not(:disabled).

These changes, and more, are demonstrated below.

example legend

example input

example email

Example telephone

example url

example number

example search

Example range

example file input

example select

Check this checkbox

Option one is this and that Option two is something else that's also super long to demonstrate the wrapping of these fancy form controls. Option three is disabled

Example textarea

example date

example time

example password

Example datetime-local

example week

Example month

example color

example output 100

date & color input support

Keep in mind date inputs are not fully supported by all browsers, namely Safari.

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 cursorchange.

Non-button element button

html

<span role="button" tabindex="0">Non-button element button</span>

misc elements

Address

The <address>element is updated to reset the browser default font-stylefrom italicto normal. line-heightis also now inherited, and margin-bottom: 1remhas 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>.

Twitter Inc.
1355 Market St, Suite 900
San Francisco, CA 94103
P: (123) 456-7890

Full Name
[email protected]

Blockquote

The default marginon blockquotes is 1em 40px, so we reset that to 0 0 1remfor something more consistent with other elements.

A well-known quote, contained in a blockquote element.

Someone famous in Source Title

Inline elements

The <abbr>element receives basic styling to make it stand out among paragraph text.

The HTML abbreviation element.

Summary

The default cursoron summary is text, so we reset that pointerto convey that the element can be interacted with by clicking on it.

Some details

More info about the details.

Even more details

Here are even more details about the details.

HTML5 `[hidden]`attributes

HTML5 adds a new global attribute named[hidden] , which is styled as display: noneby default. Borrowing an idea from PureCSS , we improve upon this default by making [hidden] { display: none !important; }to help prevent its displayfrom getting accidentally overridden.

<input type="text" hidden>

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 displayof elements.

To simply toggle the visibility of an element, meaning its displayis not modified and the element can still affect the flow of the document, use the .invisibleclass instead.

Reboot

Approach

CSS variables

Page defaults

native font stack

Headings and paragraphs

horizontal rules

Lists

Inline code

code blocks

Variables

user input

sample output

tables

Forms

date & color input support

Pointers on buttons

misc elements

Address

Blockquote

Inline elements

Summary

HTML5 [hidden]attributes

jQuery incompatibility

HTML5 `[hidden]`attributes