Reboot, a group of element-specific CSS changes in a single file, kickstart CoreUI to present an elegant, harmonious, and simple baseline to build upon.

On this page:


Reboot giving various HTML elements with slightly opinionated styles using just element selectors. Extra styling is done only with classes. For illustration, we reboot some <table> styles for a purer baseline and later provide .table, .table-bordered, and more.

Here are guidelines and goals for determining 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, generating unexpected results. More importantly though, a unique direction of margin is a simpler mental model.
  • For more comfortable scaling over device sizes, block components should use rems for margins.
  • Put declarations of font-related parts to a minimum, using inherit whenever achievable.

Page defaults

The <html> and <body> parts are renewed to provide more useful page-wide defaults. More specifically:

  • The box-sizing is globally placed on each part —including *::before and *::after, to border-box. This guarantees that the declared width of component is never passed due to padding or border.
    • No base font-size is represented on the <html>, but 16px is expected (the browser default). font-size: 1rem is applied on the <body> for easy responsive type-scaling via media queries while recognizing user favorites and assuring a more accessible way.
  • The <body> sets a global font-family, line-height, and text-align. This is acquired later by any form elements to block font inconsistencies.
  • For protection, the <body> has a declared background-color, defaulting to #fff.

Font stack

The standard web fonts (Helvetica Neue, Helvetica, and Arial) have been depraceted in the latest version of Bootstrap and replaced with a “native font stack” for best text rendering on each device and OS.

  // 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 attached to the <body> and automatically acquired globally throughout Bootstrap. To switch the global font-family, update $font-family-base and recompile Bootstrap.

Headings and paragraphs

Each heading element —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


All lists—<ul>, <ol>, and <dl>—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 better 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 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

The <pre> 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 <caption>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:

  • <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.

Example legend


Misc elements


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]


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

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.

Someone famous in Source Title

Inline elements

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

Nulla attr vitae elit libero, a pharetra augue.


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.

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. While [hidden] isn’t natively supported by IE10, the explicit declaration in our CSS gets around that problem.

<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.