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.
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 ofem
s for scalable component spacing. - Avoid
margin-top
. Vertical margins can collapse, yielding unexpected results. More importantly though, a single direction ofmargin
is a simpler mental model. - For easier scaling across device sizes, block elements should use
rem
s formargin
s. - Keep declarations of
font
-related properties to a minimum, usinginherit
whenever possible.
CSS variables
Added in v5.2.0With v5.1.1, we standardized our required @import
s 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.
For example, consider these :root
CSS variables for common <body>
styles:
@if $font-size-root != null {
--#{$prefix}root-font-size: #{$font-size-root};
}
--#{$prefix}body-font-family: #{inspect($font-family-base)};
@include rfs($font-size-base, --#{$prefix}body-font-size);
--#{$prefix}body-font-weight: #{$font-weight-base};
--#{$prefix}body-line-height: #{$line-height-base};
@if $body-text-align != null {
--#{$prefix}body-text-align: #{$body-text-align};
}
--#{$prefix}body-color: #{$body-color};
--#{$prefix}body-color-rgb: #{to-rgb($body-color)};
--#{$prefix}body-bg: #{$body-bg};
--#{$prefix}body-bg-rgb: #{to-rgb($body-bg)};
--#{$prefix}emphasis-color: #{$body-emphasis-color};
--#{$prefix}emphasis-color-rgb: #{to-rgb($body-emphasis-color)};
--#{$prefix}secondary-color: #{$body-secondary-color};
--#{$prefix}secondary-color-rgb: #{to-rgb($body-secondary-color)};
--#{$prefix}secondary-bg: #{$body-secondary-bg};
--#{$prefix}secondary-bg-rgb: #{to-rgb($body-secondary-bg)};
--#{$prefix}tertiary-color: #{$body-tertiary-color};
--#{$prefix}tertiary-color-rgb: #{to-rgb($body-tertiary-color)};
--#{$prefix}tertiary-bg: #{$body-tertiary-bg};
--#{$prefix}tertiary-bg-rgb: #{to-rgb($body-tertiary-bg)};
In practice, those variables are then applied in Reboot like so:
body {
margin: 0; // 1
font-family: var(--#{$prefix}body-font-family);
@include font-size(var(--#{$prefix}body-font-size));
font-weight: var(--#{$prefix}body-font-weight);
line-height: var(--#{$prefix}body-line-height);
color: var(--#{$prefix}body-color);
text-align: var(--#{$prefix}body-text-align);
background-color: var(--#{$prefix}body-bg); // 2
-webkit-text-size-adjust: 100%; // 3
-webkit-tap-highlight-color: rgba($black, 0); // 4
}
Which allows you to make real-time customizations however you like:
<body style="--bs-body-color: #333;">
<!-- ... -->
</body>
Page defaults
The <html>
and <body>
elements are updated to provide better page-wide defaults. More specifically:
- The
box-sizing
is globally set on every element—including*::before
and*::after
, toborder-box
. This ensures that the declared width of element is never exceeded due to padding or border.- No base
font-size
is declared on the<html>
, but16px
is assumed (the browser default).font-size: 1rem
is applied on the<body>
for easy responsive type-scaling via media queries while respecting user preferences and ensuring a more accessible approach. This browser default can be overridden by modifying the$font-size-root
variable.
- No base
- The
<body>
also sets a globalfont-family
,font-weight
,line-height
, andcolor
. This is inherited later by some form elements to prevent font inconsistencies. - For safety, the
<body>
has a declaredbackground-color
, defaulting to#fff
.
Native font stack
Bootstrap utilizes a “native font stack” or “system font stack” for optimum text rendering on every device and OS. These system fonts have been designed specifically with today’s devices in mind, with improved rendering on screens, variable font support, and more. Read more about native font stacks in this Smashing Magazine article.
$font-family-sans-serif:
// Cross-platform generic font family (default user interface font)
system-ui,
// Safari for macOS and iOS (San Francisco)
-apple-system,
// Windows
"Segoe UI",
// Android
Roboto,
// older macOS and iOS
"Helvetica Neue",
// Linux
"Noto Sans",
"Liberation Sans",
// Basic web fallback
Arial,
// Sans serif fallback
sans-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 multicolored 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
All heading elements—<h1>
—<h6>
have their margin-top
removed, margin-bottom: .5rem
set, and line-height
tightened. While headings inherit their color
by default, you can also override it via optional CSS variable, --bs-heading-color
.
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 |
Paragraphs
Alle <p>
elements have their margin-top
removed and margin-bottom: 1rem
set for easy spacing.
This is an example paragraph.
<p>This is an example paragraph.</p>
Links
Links have a default color
and underline applied. While links change on :hover
, they don’t change based on whether someone :visited
the link. They also receive no special :focus
styles.
<a href="#">This is an example link</a>
As of v5.3.x, link color
is set using rgba()
and new -rgb
CSS variables, allowing for easy customization of link color opacity. Change the link color opacity with the --bs-link-opacity
CSS variable:
<a href="#" style="--bs-link-opacity: .5">This is an example link</a>
Placeholder links—those without an href
—are targeted with a more specific selector and have their color
and text-decoration
reset to their default values.
<a>This is a placeholder link</a>
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.
- 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.
- Term
- Definition for the term.
- A second definition for the same term.
- Another term
- Definition for this other term.
Inline code
Wrap inline snippets of code with <code>
. Be sure to escape HTML angle brackets.
<section>
should be wrapped as inline.
For example, <code><section></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><p>Sample text here...</p>
<p>And another line of sample text here...</p>
</code></pre>
Variables
For indicating variables use the <var>
tag.
<var>y</var> = <var>m</var><var>x</var> + <var>b</var>
User input
Use the <kbd>
to indicate input that is typically entered via keyboard.
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.
<samp>This text is meant to be treated as sample output from a computer program.</samp>
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.
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 |
<table>
<caption>
This is an example table, and this is its caption to describe the contents.
</caption>
<thead>
<tr>
<th>Table heading</th>
<th>Table heading</th>
<th>Table heading</th>
<th>Table heading</th>
</tr>
</thead>
<tbody>
<tr>
<td>Table cell</td>
<td>Table cell</td>
<td>Table cell</td>
<td>Table cell</td>
</tr>
<tr>
<td>Table cell</td>
<td>Table cell</td>
<td>Table cell</td>
<td>Table cell</td>
</tr>
<tr>
<td>Table cell</td>
<td>Table cell</td>
<td>Table cell</td>
<td>Table cell</td>
</tr>
</tbody>
</table>
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 todisplay: inline-block
to allowmargin
to be applied.<input>
s,<select>
s,<textarea>
s, and<button>
s are mostly addressed by Normalize, but Reboot removes theirmargin
and setsline-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 havecursor: 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.
<span role="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>
.
1123 Fictional St,
San Francisco, CA 94103
P: (123) 456-7890 Full Name
first.last@example.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.
A well-known quote, contained in a blockquote element.
Someone famous in Source Title
Inline elements
The <abbr>
element receives basic styling to make it stand out amongst paragraph text.
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.
<input type="text" hidden>
[hidden]
is not compatible with jQuery’s $(...).hide()
and $(...).show()
methods, we don’t specifically 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.