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Bootstrap/site/content/docs/5.1/content/reboot.md
Louis-Maxime Piton 42162546f2
docs: A fix for CSS Variables and some proposal (#35563) 
* docs: Fix CSS variables sections

* Minor fix for dropdowns

* Minor fixes for URLs

Co-authored-by: XhmikosR <xhmikosr@gmail.com>
2021-12-18 13:53:36 +02:00

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docs 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. content /docs/5.1/content/ true

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 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.

CSS variables

Added in v5.1.1

With v5.1.1, we standardized our required @imports 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]({{< docsref "/customize/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:

{{< scss-docs name="root-body-variables" file="scss/_root.scss" >}}

In practice, those variables are then applied in Reboot like so:

{{< scss-docs name="reboot-body-rules" file="scss/_reboot.scss" >}}

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, 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. This browser default can be overridden by modifying the $font-size-root variable.
  • The <body> also sets a global font-family, font-weight, line-height, and color. 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

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,
  // Basic web fallback
  "Helvetica Neue", Arial,
  // Linux
  "Noto Sans",
  "Liberation Sans",
  // 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 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
{{< markdown >}}`

`{{< /markdown >}} 		h1. Bootstrap heading
{{< markdown >}}`

`{{< /markdown >}} 		h2. Bootstrap heading
{{< markdown >}}`

`{{< /markdown >}} 		h3. Bootstrap heading
{{< markdown >}}`

`{{< /markdown >}} 		h4. Bootstrap heading
{{< markdown >}}`
`{{< /markdown >}} 		h5. Bootstrap heading
{{< markdown >}}`
`{{< /markdown >}} 		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. We've also reset the padding-left on <ul> and <ol> elements.

{{< markdown >}} * 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
  1. Here's an ordered list
  2. With a few list items
  3. It has the same overall look
  4. As the previous unordered list {{< /markdown >}}

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.
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.

{{< example >}} For example, <section> should be wrapped as inline. {{< /example >}}

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.

{{< example >}}

<p>Sample text here...</p>
<p>And another line of sample text here...</p>

{{< /example >}}

Variables

For indicating variables use the <var> tag.

{{< example >}} y = mx + b {{< /example >}}

User input

Use the <kbd> to indicate input that is typically entered via keyboard.

{{< example >}} To switch directories, type cd followed by the name of the directory.
To edit settings, press ctrl + , {{< /example >}}

Sample output

For indicating sample output from a program use the <samp> tag.

{{< example >}} This text is meant to be treated as sample output from a computer program. {{< /example >}}

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]({{< docsref "/content/tables" >}}).

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

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.

Example legend

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

100

Button submit

Button submit

{{< callout warning >}} {{< partial "callout-warning-input-support.md" >}} {{< /callout >}}

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.

{{< example >}} Non-button element button {{< /example >}}

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
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.

The HTML abbreviation element.

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>

{{< callout warning >}}

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. {{< /callout >}}

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]({{< docsref "/utilities/visibility" >}}) instead.