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Reboot

Reboot

Part of Bootstrap’s job is to provide an elegant, consistent, and simple baseline to build upon. We use Reboot, a collection of element-specific CSS changes in a single file, to kickstart that.

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.

Contents

Approach

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

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.
  • A base font-size: 16px is declared on the <html> and font-size: 1rem on the <body> for easy responsive type-scaling via media queries.
  • The <body> also sets a global font-family and line-height. 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

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.

$font-family-sans-serif:
  // Safari for OS X and iOS (San Francisco)
  -apple-system,
  // Chrome >= 56 for OS X (San Francisco), Windows, Linux and Android
  system-ui,
  // Chrome < 56 for OS X (San Francisco)
  BlinkMacSystemFont,
  // Windows
  "Segoe UI",
  // Android
  "Roboto",
  // Basic web fallback
  "Helvetica Neue", Arial, sans-serif !default;

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 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.

Open example on getbootstrap.com

Lists

All lists—<ul>, <ol>, and <dl>—have their margin-top removed and a margin-bottom: 1rem. Nested lists have no margin-bottom.

Open example on getbootstrap.com

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.

Open example on getbootstrap.com

Preformatted text

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

Open example on getbootstrap.com

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.

Open example on getbootstrap.com

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.

These changes, and more, are demonstrated below.

Open example on getbootstrap.com

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>.

Open example on getbootstrap.com

Blockquote

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

Open example on getbootstrap.com

Inline elements

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

Open example on getbootstrap.com

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. This could potentially change in jQuery 3, but we’re not holding our breath. 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.

Click delay optimization for touch

Traditionally, browsers on touchscreen devices have a delay of approximately 300ms between the end of a “tap” – the moment when a finger/stylus is lifted from screen – and the click event being fired. This delay is necessary for these browsers to correctly handle “double-tap to zoom” gestures without prematurely triggering actions or links after the first “tap”, but it can make your site feel slightly sluggish and unresponsive.

Most mobile browsers automatically optimize away this 300ms delay for sites that use the width=device-width property as part of their responsive meta tag (as well as for sites that disable zooming, for instance with user-scalable=no, though this practice is strongly discouraged for accessibility and usability reasons). The biggest exceptions here are IE11 on Windows Phone 8.1, and iOS Safari (and any other iOS WebView-based browser) prior to iOS 9.3.

On touch-enabled laptop/desktop devices, IE11 and Microsoft Edge are currently the only browsers with “double-tap to zoom” functionality. As the responsive meta tag is ignored by all desktop browsers, using width=device-width will have no effect on the 300ms delay here.

To address this problem in IE11 and Microsoft Edge on desktop, as well as IE11 on Windows Phone 8.1, Bootstrap explicitly uses the touch-action:manipulation CSS property on all interactive elements (such as buttons and links). This property essentially disables double-tap functionality on those elements, eliminating the 300ms delay.

In the case of old iOS versions (prior to 9.3), the suggested approach is to use additional scripts such as FastClick to explicitly work around the delay.

For further details, see the compatibility table for suppressing 300ms delay for touchscreen interactions.

doc_bootstrap
doc_bootstrap
2017-01-24 08:45:55
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