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338 lines
14 KiB
Markdown
338 lines
14 KiB
Markdown
---
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layout: docs
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title: Reboot
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group: content
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redirect_from: "/content/"
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---
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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.
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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.
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## Contents
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* Will be replaced with the ToC, excluding the "Contents" header
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{:toc}
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## Approach
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Here are our guidelines and reasons for choosing what to override in Reboot:
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- Update some browser default values to use `rem`s instead of `em`s for scalable component spacing.
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- Avoid `margin-top`. Vertical margins can collapse, yielding unexpected results. More importantly though, a single direction of `margin` is a simpler mental model.
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- For easier scaling across device sizes, block elements should use `rem`s for `margin`s.
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- Keep declarations of `font`-related properties to a minimum, using `inherit` whenever possible.
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## Page defaults
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The `<html>` and `<body>` elements are updated to provide better page-wide defaults. More specifically:
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- 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.
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- 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.
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- The `<body>` also sets a global `font-family` and `line-height`. This is inherited later by some form elements to prevent font inconsistencies.
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- For safety, the `<body>` has a declared `background-color`, defaulting to `#fff`.
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## Native font stack
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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](https://www.smashingmagazine.com/2015/11/using-system-ui-fonts-practical-guide/).
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{% highlight sass %}
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$font-family-sans-serif:
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// Safari for OS X and iOS (San Francisco)
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-apple-system,
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// Chrome for OS X (San Francisco)
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BlinkMacSystemFont,
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// Windows
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"Segoe UI",
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// Android
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"Roboto",
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// Basic web fallback
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"Helvetica Neue", Arial, sans-serif !default;
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{% endhighlight %}
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This `font-family` is applied to the `<body>` and automatically inherited globally throughout Bootstrap. To switch the global `font-family`, update `$font-family-base` and recompile Bootstrap.
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## Headings and paragraphs
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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.
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<div class="bd-example">
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{% markdown %}
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# h1 heading
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Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
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## h2 heading
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Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
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### h3 heading
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Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
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#### h4 heading
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Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
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##### h5 heading
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Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
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###### h6 heading
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Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
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{% endmarkdown %}
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</div>
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## Lists
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All lists—`<ul>`, `<ol>`, and `<dl>`—have their `margin-top` removed and a `margin-bottom: 1rem`. Nested lists have no `margin-bottom`.
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<div class="bd-example">
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{% markdown %}
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* Lorem ipsum dolor sit amet
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* Consectetur adipiscing elit
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* Integer molestie lorem at massa
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* Facilisis in pretium nisl aliquet
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* Nulla volutpat aliquam velit
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* Phasellus iaculis neque
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* Purus sodales ultricies
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* Vestibulum laoreet porttitor sem
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* Ac tristique libero volutpat at
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* Faucibus porta lacus fringilla vel
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* Aenean sit amet erat nunc
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* Eget porttitor lorem
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1. Lorem ipsum dolor sit amet
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2. Consectetur adipiscing elit
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3. Integer molestie lorem at massa
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4. Facilisis in pretium nisl aliquet
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5. Nulla volutpat aliquam velit
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6. Faucibus porta lacus fringilla vel
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7. Aenean sit amet erat nunc
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8. Eget porttitor lorem
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{% endmarkdown %}
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</div>
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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**.
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<div class="bd-example">
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{% markdown %}
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<dl>
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<dt>Description lists</dt>
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<dd>A description list is perfect for defining terms.</dd>
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<dt>Euismod</dt>
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<dd>Vestibulum id ligula porta felis euismod semper eget lacinia odio sem.</dd>
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<dd>Donec id elit non mi porta gravida at eget metus.</dd>
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<dt>Malesuada porta</dt>
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<dd>Etiam porta sem malesuada magna mollis euismod.</dd>
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</dl>
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{% endmarkdown %}
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</div>
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## Preformatted text
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The `<pre>` element is reset to remove its `margin-top` and use `rem` units for its `margin-bottom`.
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<div class="bd-example">
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{% markdown %}
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<pre>
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.example-element {
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margin-bottom: 1rem;
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}
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</pre>
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{% endmarkdown %}
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</div>
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## Tables
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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]({{ site.baseurl }}/content/tables/).
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<div class="bd-example">
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<table>
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<caption>
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This is an example table, and this is its caption to describe the contents.
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</caption>
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<thead>
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<tr>
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<th>Table heading</th>
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<th>Table heading</th>
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<th>Table heading</th>
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<th>Table heading</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>Table cell</td>
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<td>Table cell</td>
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<td>Table cell</td>
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<td>Table cell</td>
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</tr>
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<tr>
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<td>Table cell</td>
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<td>Table cell</td>
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<td>Table cell</td>
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<td>Table cell</td>
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</tr>
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<tr>
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<td>Table cell</td>
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<td>Table cell</td>
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<td>Table cell</td>
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<td>Table cell</td>
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</tr>
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</tbody>
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</table>
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</div>
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## Forms
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Various form elements have been rebooted for simpler base styles. Here are some of the most notable changes:
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- `<fieldset>`s have no borders, padding, or margin so they can be easily used as wrappers for individual inputs or groups of inputs.
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- `<legend>`s, like fieldsets, have also been restyled to be displayed as a heading of sorts.
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- `<label>`s are set to `display: inline-block` to allow `margin` to be applied.
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- `<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.
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- `<textarea>`s are modified to only be resizable vertically as horizontal resizing often "breaks" page layout.
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These changes, and more, are demonstrated below.
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<form class="bd-example">
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<fieldset>
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<legend>Example legend</legend>
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<p>
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<label for="input">Example input</label>
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<input type="text" id="input" placeholder="Example input">
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</p>
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<p>
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<label for="select">Example select</label>
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<select id="select">
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<option value="">Choose...</option>
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<optgroup label="Option group 1">
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<option value="">Option 1</option>
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<option value="">Option 2</option>
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<option value="">Option 3</option>
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</optgroup>
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<optgroup label="Option group 2">
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<option value="">Option 4</option>
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<option value="">Option 5</option>
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<option value="">Option 6</option>
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</optgroup>
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</select>
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</p>
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<p>
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<label>
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<input type="checkbox" value="">
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Check this checkbox
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</label>
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</p>
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<p>
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<label>
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<input type="radio" name="optionsRadios" id="optionsRadios1" value="option1" checked>
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Option one is this and that
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</label>
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<label>
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<input type="radio" name="optionsRadios" id="optionsRadios2" value="option2">
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Option two is something else that's also super long to demonstrate the wrapping of these fancy form controls.
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</label>
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<label>
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<input type="radio" name="optionsRadios" id="optionsRadios3" value="option3" disabled>
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Option three is disabled
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</label>
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</p>
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<p>
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<label for="textarea">Example textarea</label>
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<textarea id="textarea" rows="3"></textarea>
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</p>
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<p>
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<label for="time">Example temporal</label>
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<input type="datetime-local" id="time">
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</p>
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<p>
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<label for="output">Example output</label>
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<output name="result" id="output">100</output>
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</p>
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<p>
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<button type="submit">Button submit</button>
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<input type="submit" value="Input submit button">
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<input type="button" value="Input button">
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</p>
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<p>
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<button type="submit" disabled>Button submit</button>
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<input type="submit" value="Input submit button" disabled>
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<input type="button" value="Input button" disabled>
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</p>
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</fieldset>
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</form>
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## Misc elements
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### Address
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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>`.
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<div class="bd-example">
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<address>
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<strong>Twitter, Inc.</strong><br>
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1355 Market St, Suite 900<br>
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San Francisco, CA 94103<br>
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<abbr title="Phone">P:</abbr> (123) 456-7890
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</address>
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<address>
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<strong>Full Name</strong><br>
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<a href="mailto:#">first.last@example.com</a>
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</address>
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</div>
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### Blockquote
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The default `margin` on blockquotes is `1em 40px`, so we reset that to `0 0 1rem` for something more consistent with other elements.
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<div class="bd-example">
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<blockquote class="blockquote">
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<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
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<footer>Someone famous in <cite title="Source Title">Source Title</cite></footer>
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</blockquote>
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</div>
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### Inline elements
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The `<abbr>` element receives basic styling to make it stand out amongst paragraph text.
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<div class="bd-example">
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Nulla <abbr title="attribute">attr</abbr> vitae elit libero, a pharetra augue.
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</div>
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## HTML5 `[hidden]` attribute
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HTML5 adds [a new global attribute named `[hidden]`](https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/hidden), which is styled as `display: none` by default. Borrowing an idea from [PureCSS](http://purecss.io), 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 IE9-10, the explicit declaration in our CSS gets around that problem.
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{% highlight html %}
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<input type="text" hidden>
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{% endhighlight %}
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{% callout warning %}
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#### jQuery incompatibility
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`[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.
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{% endcallout %}
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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]({{ site.baseurl }}/components/utilities/#invisible-content) instead.
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## Click delay optimization for touch
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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](https://developer.mozilla.org/en-US/docs/Web/Events/click) 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.
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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]({{ site.baseurl }}/getting-started/introduction/#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](https://webkit.org/blog/5610/more-responsive-tapping-on-ios/).
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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]({{ site.baseurl }}/getting-started/introduction/#responsive-meta-tag) is ignored by all desktop browsers, using `width=device-width` will have no effect on the 300ms delay here.
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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](https://developer.mozilla.org/en-US/docs/Web/CSS/touch-action) on all interactive elements (such as buttons and links). This property essentially disables double-tap functionality on those elements, eliminating the 300ms delay.
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In the case of old iOS versions (prior to 9.3), the suggested approach is to use additional scripts such as [FastClick](https://github.com/ftlabs/fastclick) to explicitly work around the delay.
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For further details, see the compatibility table for [suppressing 300ms delay for touchscreen interactions](http://patrickhlauke.github.io/touch/tests/results/#suppressing-300ms-delay).
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