For improved cross-browser rendering, we use Reboot to correct inconsistencies across browsers and devices while providing slightly more opinionated resets to common HTML elements.

Overview

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 Bootstrap 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.

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.

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.

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

<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-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.

Unordered list

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

<ul>
  <li>All lists have their top margin removed</li>
  <li>And their bottom margin normalized</li>
  <li>
    Nested lists have no bottom margin
    <ul>
      <li>This way they have a more even appearance</li>
      <li>Particularly when followed by more list items</li>
    </ul>
  </li>
  <li>The left padding has also been reset</li>
</ul>

Ordered list

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

<ol>
  <li>Here’s an ordered list</li>
  <li>With a few list items</li>
  <li>It has the same overall look</li>
  <li>As the previous unordered list</li>
</ol>

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.

Description list

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.

<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>

Unstyled

Remove the default list-style and left margin on list items (immediate children only). This only applies to immediate children list items, meaning you will need to add the class for any nested lists as well.

This is a list.
It appears completely unstyled.
Structurally, it's still a list.
However, this style only applies to immediate child elements.
Nested lists:
- are unaffected by this style
- will still show a bullet
- and have appropriate left margin
This may still come in handy in some situations.

<ul class="list-unstyled">
  <li>This is a list.</li>
  <li>It appears completely unstyled.</li>
  <li>Structurally, it's still a list.</li>
  <li>However, this style only applies to immediate child elements.</li>
  <li>Nested lists:
    <ul>
      <li>are unaffected by this style</li>
      <li>will still show a bullet</li>
      <li>and have appropriate left margin</li>
    </ul>
  </li>
  <li>This may still come in handy in some situations.</li>
</ul>

Inline items

Remove a list’s bullets and apply some light margin with a combination of two classes, .list-inline and .list-inline-item.

This is a list item.
And another one.
But they're displayed inline.

<ul class="list-inline">
  <li class="list-inline-item text-primary">This is a list item.</li>
  <li class="list-inline-item text-secondary">And another one.</li>
  <li class="list-inline-item text-success">But they're displayed inline.</li>
</ul>

Inline code

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

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

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-top and use rem units for its margin-bottom.

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

<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 = mx + b

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

Inline text elements

Styling for common inline HTML5 elements.

You can use the mark tag to highlight text.

~~This line of text is meant to be treated as deleted text.~~

~~This line of text is meant to be treated as no longer accurate.~~

This line of text is meant to be treated as an addition to the document.

This line of text will render as underlined.

This line of text is meant to be treated as fine print.

This line rendered as bold text.

This line rendered as italicized text.

<p>You can use the mark tag to <mark>highlight</mark> text.</p>
<p><del>This line of text is meant to be treated as deleted text.</del></p>
<p><s>This line of text is meant to be treated as no longer accurate.</s></p>
<p><ins>This line of text is meant to be treated as an addition to the document.</ins></p>
<p><u>This line of text will render as underlined.</u></p>
<p><small>This line of text is meant to be treated as fine print.</small></p>
<p><strong>This line rendered as bold text.</strong></p>
<p><em>This line rendered as italicized text.</em></p>

Beware that those tags should be used for semantic purpose:

<mark> represents text which is marked or highlighted for reference or notation purposes.
<small> represents side-comments and small print, like copyright and legal text.
<s> represents element that are no longer relevant or no longer accurate.
<u> represents a span of inline text which should be rendered in a way that indicates that it has a non-textual annotation.

If you want to style your text, you should use the following classes instead:

.mark will apply the same styles as <mark>.
.small will apply the same styles as <small>.
.text-decoration-underline will apply the same styles as <u>.
.text-decoration-line-through will apply the same styles as <s>.

While not shown above, feel free to use <b> and <i> in HTML5. <b> is meant to highlight words or phrases without conveying additional importance, while <i> is mostly for voice, technical terms, etc.

User input

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

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

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.

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

Table

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 component.

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:

<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).

See Form component

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.

Non-button element button

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

Abbreviations

Stylized implementation of HTML’s <abbr> element for abbreviations and acronyms to show the expanded version on hover. Abbreviations have a default underline and gain a help cursor to provide additional context on hover and to users of assistive technologies.

Add .initialism to an abbreviation for a slightly smaller font-size.

attr

HTML

<p><abbr title="attribute">attr</abbr></p>
<p><abbr title="HyperText Markup Language" class="initialism">HTML</abbr></p>

Blockquote

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

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

Someone famous in Source Title

<blockquote class="blockquote">
  <p>A well-known quote, contained in a blockquote element.</p>
</blockquote>
<p>Someone famous in <cite title="Source Title">Source Title</cite></p>

Naming a source

The HTML spec requires that blockquote attribution be placed outside the <blockquote>. When providing attribution, wrap your <blockquote> in a <figure> and use a <figcaption> or a block level element (e.g., <p>) with the .blockquote-footer class. Be sure to wrap the name of the source work in <cite> as well.

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

<figure>
  <blockquote class="blockquote">
    <p>A well-known quote, contained in a blockquote element.</p>
  </blockquote>
  <figcaption class="blockquote-footer">
    Someone famous in <cite title="Source Title">Source Title</cite>
  </figcaption>
</figure>

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>.

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

Full Name
[email protected]

<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:[email protected]">[email protected]</a>
</address>

Inline elements

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

The HTML abbreviation element.

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.

Some details

More info about the details.

Even more details

Here are even more details about the details.

<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.

<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 display of elements.

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.

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Last updated on April 6, 2024

Reboot