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.
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
rem
s instead of
em
s 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
rem
s for
margin
s.
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.
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.
The
<body>
also sets a global
font-family
,
line-height
, and
text-align
. 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 macOS and iOS (San Francisco)-apple-system,// Chrome < 56 for macOS (San Francisco)BlinkMacSystemFont,// Windows"Segoe UI",// AndroidRoboto,// Basic web fallback"Helvetica Neue",Arial,// Linux"Noto Sans","Liberation Sans",// Sans serif fallbacksans-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 multi-colored 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 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
Lists
All lists—
<ul>
,
<ol>
, and
<dl>
—have their
margin-top
removed and a
margin-bottom: 1rem
. Nested lists have no
margin-bottom
.
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
For simpler styling, clear hierarchy, and better spacing, description lists have updated
margin
s.
<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.
Definition for the term.
A second definition for the same term.
Another term
Definition for this other term.
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
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
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.
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
<spanrole="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
<br>
.
Twitter, Inc.
1355 Market St, Suite 900
San Francisco, CA 94103
P:
(123) 456-7890
Full Name
[email protected]
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.
Inline elements
The
<abbr>
element receives basic styling to make it stand out amongst paragraph text.
Nulla
attr
vitae elit libero, a pharetra augue.
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.
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.
<inputtype="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.
