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Learn Bootstrap 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.


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  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.

Page defaults



 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 , but 16px is assumed (the browser default). font-size: 1rem is applied on the  for easy responsive type-scaling via media queries while respecting user preferences and ensuring a more accessible approach.
  • The  also sets a global font-familyline-height, and text-align. This is inherited later by some form elements to prevent font inconsistencies.
  • For safety, the  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.

  // Safari for macOS and iOS (San Francisco)
  // Chrome < 56 for macOS (San Francisco)
  // Windows
  "Segoe UI",
  // Android
  // Basic web fallback
  "Helvetica Neue", Arial, sans-serif,
  // Emoji fonts
  "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol" !default;

This font-family is applied to the 

 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., 


 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. Bootstrap heading




h2. Bootstrap heading




h3. Bootstrap heading



h4. Bootstrap heading



h5. Bootstrap heading



h6. Bootstrap heading


All lists—

    1. , and —have their margin-top removed and a margin-bottom: 1rem. Nested lists have no margin-bottom.


      • Lorem ipsum dolor sit amet
      • Consectetur adipiscing elit
      • Integer molestie lorem at massa
      • Facilisis in pretium nisl aliquet
      • Nulla volutpat aliquam velit
        • Phasellus iaculis neque
        • Purus sodales ultricies
        • Vestibulum laoreet porttitor sem
        • Ac tristique libero volutpat at
      • Faucibus porta lacus fringilla vel
      • Aenean sit amet erat nunc
      • Eget porttitor lorem
      1. Lorem ipsum dolor sit amet
      2. Consectetur adipiscing elit
      3. Integer molestie lorem at massa
      4. Facilisis in pretium nisl aliquet
      5. Nulla volutpat aliquam velit
      6. Faucibus porta lacus fringilla vel
      7. Aenean sit amet erat nunc
      8. Eget porttitor lorem

      For simpler styling, clear hierarchy, and better spacing, description lists have updated margins. 

      s reset margin-left to 0 and add margin-bottom: .5rem

      s are bolded.


      Description lists

      A description list is perfect for defining terms.


      Vestibulum id ligula porta felis euismod semper eget lacinia odio sem.

      Donec id elit non mi porta gravida at eget metus.

      Malesuada porta

      Etiam porta sem malesuada magna mollis euismod.

      Preformatted text


       element is reset to remove its margin-top and use rem units for its margin-bottom.


      .example-element {
        margin-bottom: 1rem;


      Tables are slightly adjusted to style s, collapse borders, and ensure consistent text-align throughout. Additional changes for borders, padding, and more come with the .table class.

      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


      Various form elements have been rebooted for simpler base styles. Here are some of the most notable changes:

      • s have no borders, padding, or margin so they can be easily used as wrappers for individual inputs or groups of inputs.

      • s, like fieldsets, have also been restyled to be displayed as a heading of sorts.
      • s are set to display: inline-block to allow margin to be applied.
      • s, s, </code>s, and <code><button></code>s are mostly addressed by Normalize, but Reboot removes their <code>margin</code> and sets <code>line-height: inherit</code>, too.</li> <li><code><textarea></code>s are modified to only be resizable vertically as horizontal resizing often “breaks” page layout.</li> <li><code><button></code>s and <code><input></code> button elements have <code>cursor: pointer</code> when <code>:not(:disabled)</code>.</li> </ul> <p>These changes, and more, are demonstrated below.</p> <p>Example legend</p> <p>Example input </p> <p>Example select          Choose...                    Option 1           Option 2           Option 3                             Option 4           Option 5           Option 6                </p> <p> Check this checkbox</p> <p> 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</p> <p>Example textarea </p> <p>Example date </p> <p>Example time </p> <p>Example output 100</p> <p>Button submit   </p> <p>Button submit   </p> <h2>Misc elements</h2> <h3>Address</h3> <p>The <code><address></code> element is updated to reset the browser default <code>font-style</code> from <code>italic</code> to <code>normal</code>. <code>line-height</code> is also now inherited, and <code>margin-bottom: 1rem</code> has been added. <code><address></code>s are for presenting contact information for the nearest ancestor (or an entire body of work). Preserve formatting by ending lines with <code><br></code>.</p> <p><strong>Twitter, Inc.</strong><br /> 1355 Market St, Suite 900<br /> San Francisco, CA 94103<br /> P: (123) 456-7890</p> <p><strong>Full Name</strong><br /> <a data-cke-saved-href="" href=""></a></p> <h3>Blockquote</h3> <p>The default <code>margin</code> on blockquotes is <code>1em 40px</code>, so we reset that to <code>0 0 1rem</code> for something more consistent with other elements.</p> <blockquote> <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p> <p>Someone famous in <cite>Source Title</cite></p> </blockquote> <h3>Inline elements</h3> <p>The <code><abbr></code> element receives basic styling to make it stand out amongst paragraph text.</p> <p>Nulla attr vitae elit libero, a pharetra augue.</p> <h3>Summary</h3> <p>The default <code>cursor</code> on summary is <code>text</code>, so we reset that to <code>pointer</code> to convey that the element can be interacted with by clicking on it.</p> <p>Some details</p> <p>Even more details</p> <p>Here are even more details about the details.</p> <h2>HTML5 <code>[hidden]</code> attribute</h2> <p>HTML5 adds <a data-cke-saved-href="" href="">a new global attribute named <code>[hidden]</code></a>, which is styled as <code>display: none</code> by default. Borrowing an idea from <a data-cke-saved-href="" href="">PureCSS</a>, we improve upon this default by making <code>[hidden] { display: none !important; }</code> to help prevent its <code>display</code> from getting accidentally overridden. While <code>[hidden]</code> isn’t natively supported by IE10, the explicit declaration in our CSS gets around that problem.</p> <pre> <code><input type="text" hidden></code></pre> <p>jQuery incompatibility</p> <p><code>[hidden]</code> is not compatible with jQuery’s <code>$(...).hide()</code> and <code>$(...).show()</code> methods. Therefore, we don’t currently especially endorse <code>[hidden]</code> over other techniques for managing the <code>display</code> of elements.</p> <p>To merely toggle the visibility of an element, meaning its <code>display</code> is not modified and the element can still affect the flow of the document, use <a data-cke-saved-href="" href="">the <code>.invisible</code> class</a> instead.</p>

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