Reboot

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 margin is 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 inherit whenever possible.

CSS variables

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 :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, 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 :root CSS variables for common <body> styles:

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

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

html

<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-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. This browser default can be overridden by modifying the $font-size-root variable.
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.

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,
  // 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 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

All heading elements—<h1>—<h6> have their margin-top removed, margin-bottom: .5rem set, and line-height tightened. While headings inherit their color by default, you can also override it via optional CSS variable, --bs-heading-color.

<BsTable> | Heading | Example | | --- | --- | | `<h1></h1>` | <span class="h1">h1. Bootstrap heading</span> | | `<h2></h2>` | <span class="h2">h2. Bootstrap heading</span> | | `<h3></h3>` | <span class="h3">h3. Bootstrap heading</span> | | `<h4></h4>` | <span class="h4">h4. Bootstrap heading</span> | | `<h5></h5>` | <span class="h5">h5. Bootstrap heading</span> | | `<h6></h6>` | <span class="h6">h6. Bootstrap heading</span> | </BsTable>

Paragraphs

All <p> elements have their margin-top removed and margin-bottom: 1rem set for easy spacing.

<Example code={<p>This is an example paragraph.</p>} />

Links

Links have a default color and underline applied. While links change on :hover, they don’t change based on whether someone :visited the link. They also receive no special :focus styles.

<Example code={<a href="#">This is an example link</a>} />

As of v5.3.x, link color is set using rgba() and new -rgb CSS variables, allowing for easy customization of link color opacity. Change the link color opacity with the --bs-link-opacity CSS variable:

<Example code={<a href="#" style="--bs-link-opacity: .5">This is an example link</a>} />

Placeholder links—those without an href—are targeted with a more specific selector and have their color and text-decoration reset to their default values.

<Example code={<a>This is a placeholder link</a>} />

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-color via color, including when color is set via the parent. They can be modified with text, border, and opacity utilities.

Lists

All lists—<ul>, <ol>, and <dl>—have their margin-top removed and a margin-bottom: 1rem. Nested lists have no margin-bottom. We’ve also reset the padding-left on <ul> and <ol> elements.

<div class="bd-example"> * 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

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

</div>

For simpler styling, clear hierarchy, and better spacing, description lists have updated margins. <dd>s reset margin-left to 0 and add margin-bottom: .5rem. <dt>s are bolded.

<Example showMarkup={false} code={`

<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> `} />

Inline code

Wrap inline snippets of code with <code>. Be sure to escape HTML angle brackets.

<Example code={For example, <code><section></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-top and use rem units for its margin-bottom.

<Example code={<pre><code><p>Sample text here...</p> <p>And another line of sample text here...</p> </code></pre>} />

Variables

For indicating variables use the <var> tag.

User input

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

<Example code={`To switch directories, type <kbd>cd</kbd> followed by the name of the directory.

To edit settings, press <kbd><kbd>Ctrl</kbd> + <kbd>,</kbd></kbd>`} />

Sample output

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

<Example code={<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-align throughout. Additional changes for borders, padding, and more come with the .table class.

<Example code={`<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-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.

<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="[email protected]"/> </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"></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="password">Example password</label> <input type="password" id="password"/> </p> <p> <label for="datetime-local">Example datetime-local</label> <input type="datetime-local" id="datetime-local"/> </p> <p> <label for="week">Example week</label> <input type="week" id="week"/> </p> <p> <label for="month">Example month</label> <input type="month" id="month"/> </p> <p> <label for="color">Example color</label> <input type="color" id="color"/> </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 code={<span role="button" tabindex="0">Non-button element button</span>} />

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 .

<Example showMarkup={false} code={`<address> <strong>ACME Corporation</strong>

1123 Fictional St,

San Francisco, CA 94103

<abbr title="Phone">P:</abbr> (123) 456-7890

</address> <address> <strong>Full Name</strong>

<a href="mailto:[email protected]">[email protected]</a>

</address>`} />

Blockquote

The default margin on blockquotes is 1em 40px, so we reset that to 0 0 1rem for something more consistent with other elements.

<Example showMarkup={false} code={`<figure> <blockquote class="blockquote"> <p>A well-known quote, contained in a blockquote element.</p> </blockquote> <figcaption> Someone famous in <cite title="Source Title">Source Title</cite> </figcaption>

</figure>`} />

Inline elements

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

<Example showMarkup={false} code={The <abbr title="HyperText Markup Language">HTML</abbr> abbreviation element.} />

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.

<Example showMarkup={false} code={`

<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> `} />

HTML5 `[hidden]` attribute

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

html

<input type="text" hidden>

<Callout> Since `[hidden]` is not compatible with jQuery’s `$(...).hide()` and `$(...).show()` methods, we don’t specifically 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 instead.

Approach

CSS variables

Page defaults

Native font stack

Headings

Paragraphs

Links

Horizontal rules

Lists

Inline code

Code blocks

Variables

User input

Sample output

Tables

Forms

Pointers on buttons

Misc elements

Address

Blockquote

Inline elements

Summary

HTML5 [hidden] attribute

HTML5 `[hidden]` attribute