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:
rems instead of ems for scalable component spacing.margin-top. Vertical margins can collapse, yielding unexpected results. More importantly though, a single direction of margin is a simpler mental model.rems for margins.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:
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.
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.<body> also sets a global font-family, line-height, and text-align. This is inherited later by some form elements to prevent font inconsistencies.<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.
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$font-family-sans-serif:
// Safari for OS X and iOS (San Francisco)
-apple-system,
// Chrome < 56 for OS X (San Francisco)
BlinkMacSystemFont,
// Windows
"Segoe UI",
// Android
"Roboto",
// 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 <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 |
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h1. Bootstrap heading |
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h2. Bootstrap heading |
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h3. Bootstrap heading |
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h4. Bootstrap heading |
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h5. Bootstrap heading |
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h6. Bootstrap heading |
Lists
All lists—<ul>, <ol>, and <dl>—have their margin-top removed and a margin-bottom: 1rem. Nested lists have no margin-bottom.
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.
Description lists
A description list is perfect for defining terms.
Euismod
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
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 .tableclass.
| 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 |
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.
Example legend
Example input
Example select Choose... Option 1 Option 2 Option 3 Option 4 Option 5 Option 6
Check this checkbox
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
Example textarea
Example date
Example time
Example output 100
Button submit
Button submit
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>.
Blockquote
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.
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
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.
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<input type="text" hidden>[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.
