src/scss/bootstrap-4.0.0-alpha.6/docs/content/reboot.md

   1 ---
   2 layout: docs
   3 title: Reboot
   4 description: Documentation and examples for Reboot, Bootstrap's collection of element-specific CSS that builds on Normalize.css.
   5 group: content
   6 redirect_from: "/content/"
   7 ---
   8
   9 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.
  10
  11 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.
  12
  13 ## Contents
  14
  15 * Will be replaced with the ToC, excluding the "Contents" header
  16 {:toc}
  17
  18 ## Approach
  19
  20 Here are our guidelines and reasons for choosing what to override in Reboot:
  21
  22 - Update some browser default values to use `rem`s instead of `em`s for scalable component spacing.
  23 - Avoid `margin-top`. Vertical margins can collapse, yielding unexpected results. More importantly though, a single direction of `margin` is a simpler mental model.
  24 - For easier scaling across device sizes, block elements should use `rem`s for `margin`s.
  25 - Keep declarations of `font`-related properties to a minimum, using `inherit` whenever possible.
  26
  27 ## Page defaults
  28
  29 The `<html>` and `<body>` elements are updated to provide better page-wide defaults. More specifically:
  30
  31 - 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.
  32 - 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.
  33 - The `<body>` also sets a global `font-family` and `line-height`. This is inherited later by some form elements to prevent font inconsistencies.
  34 - For safety, the `<body>` has a declared `background-color`, defaulting to `#fff`.
  35
  36 ## Native font stack
  37
  38 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/).
  39
  40 {% highlight sass %}
  41 $font-family-sans-serif:
  42   // Safari for OS X and iOS (San Francisco)
  43   -apple-system,
  44   // Chrome >= 56 for OS X (San Francisco), Windows, Linux and Android
  45   system-ui,
  46   // Chrome < 56 for OS X (San Francisco)
  47   BlinkMacSystemFont,
  48   // Windows
  49   "Segoe UI",
  50   // Android
  51   "Roboto",
  52   // Basic web fallback
  53   "Helvetica Neue", Arial, sans-serif !default;
  54 {% endhighlight %}
  55
  56 This `font-family` is applied to the `<body>` and automatically inherited globally throughout Bootstrap. To switch the global `font-family`, update `$font-family-base` and recompile Bootstrap.
  57
  58 ## Headings and paragraphs
  59
  60 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.
  61
  62 <div class="bd-example">
  63 {% markdown %}
  64 # h1 heading
  65 Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
  66
  67 ## h2 heading
  68 Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
  69
  70 ### h3 heading
  71 Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
  72
  73 #### h4 heading
  74 Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
  75
  76 ##### h5 heading
  77 Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
  78
  79 ###### h6 heading
  80 Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.
  81 {% endmarkdown %}
  82 </div>
  83
  84 ## Lists
  85
  86 All lists—`<ul>`, `<ol>`, and `<dl>`—have their `margin-top` removed and a `margin-bottom: 1rem`. Nested lists have no `margin-bottom`.
  87
  88 <div class="bd-example">
  89 {% markdown %}
  90 * Lorem ipsum dolor sit amet
  91 * Consectetur adipiscing elit
  92 * Integer molestie lorem at massa
  93 * Facilisis in pretium nisl aliquet
  94 * Nulla volutpat aliquam velit
  95   * Phasellus iaculis neque
  96   * Purus sodales ultricies
  97   * Vestibulum laoreet porttitor sem
  98   * Ac tristique libero volutpat at
  99 * Faucibus porta lacus fringilla vel
 100 * Aenean sit amet erat nunc
 101 * Eget porttitor lorem
 102
 103 1. Lorem ipsum dolor sit amet
 104 2. Consectetur adipiscing elit
 105 3. Integer molestie lorem at massa
 106 4. Facilisis in pretium nisl aliquet
 107 5. Nulla volutpat aliquam velit
 108 6. Faucibus porta lacus fringilla vel
 109 7. Aenean sit amet erat nunc
 110 8. Eget porttitor lorem
 111 {% endmarkdown %}
 112 </div>
 113
 114 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**.
 115
 116 <div class="bd-example">
 117 {% markdown %}
 118 <dl>
 119   <dt>Description lists</dt>
 120   <dd>A description list is perfect for defining terms.</dd>
 121   <dt>Euismod</dt>
 122   <dd>Vestibulum id ligula porta felis euismod semper eget lacinia odio sem.</dd>
 123   <dd>Donec id elit non mi porta gravida at eget metus.</dd>
 124   <dt>Malesuada porta</dt>
 125   <dd>Etiam porta sem malesuada magna mollis euismod.</dd>
 126 </dl>
 127 {% endmarkdown %}
 128 </div>
 129
 130 ## Preformatted text
 131
 132 The `<pre>` element is reset to remove its `margin-top` and use `rem` units for its `margin-bottom`.
 133
 134 <div class="bd-example">
 135 {% markdown %}
 136 <pre>
 137 .example-element {
 138   margin-bottom: 1rem;
 139 }
 140 </pre>
 141 {% endmarkdown %}
 142 </div>
 143
 144 ## Tables
 145
 146 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/).
 147
 148 <div class="bd-example">
 149   <table>
 150     <caption>
 151       This is an example table, and this is its caption to describe the contents.
 152     </caption>
 153     <thead>
 154       <tr>
 155         <th>Table heading</th>
 156         <th>Table heading</th>
 157         <th>Table heading</th>
 158         <th>Table heading</th>
 159       </tr>
 160     </thead>
 161     <tbody>
 162       <tr>
 163         <td>Table cell</td>
 164         <td>Table cell</td>
 165         <td>Table cell</td>
 166         <td>Table cell</td>
 167       </tr>
 168       <tr>
 169         <td>Table cell</td>
 170         <td>Table cell</td>
 171         <td>Table cell</td>
 172         <td>Table cell</td>
 173       </tr>
 174       <tr>
 175         <td>Table cell</td>
 176         <td>Table cell</td>
 177         <td>Table cell</td>
 178         <td>Table cell</td>
 179       </tr>
 180     </tbody>
 181   </table>
 182 </div>
 183
 184 ## Forms
 185
 186 Various form elements have been rebooted for simpler base styles. Here are some of the most notable changes:
 187
 188 - `<fieldset>`s have no borders, padding, or margin so they can be easily used as wrappers for individual inputs or groups of inputs.
 189 - `<legend>`s, like fieldsets, have also been restyled to be displayed as a heading of sorts.
 190 - `<label>`s are set to `display: inline-block` to allow `margin` to be applied.
 191 - `<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.
 192 - `<textarea>`s are modified to only be resizable vertically as horizontal resizing often "breaks" page layout.
 193
 194 These changes, and more, are demonstrated below.
 195
 196 <form class="bd-example">
 197   <fieldset>
 198     <legend>Example legend</legend>
 199
 200     <p>
 201       <label for="input">Example input</label>
 202       <input type="text" id="input" placeholder="Example input">
 203     </p>
 204
 205     <p>
 206       <label for="select">Example select</label>
 207       <select id="select">
 208         <option value="">Choose...</option>
 209         <optgroup label="Option group 1">
 210           <option value="">Option 1</option>
 211           <option value="">Option 2</option>
 212           <option value="">Option 3</option>
 213         </optgroup>
 214         <optgroup label="Option group 2">
 215           <option value="">Option 4</option>
 216           <option value="">Option 5</option>
 217           <option value="">Option 6</option>
 218         </optgroup>
 219       </select>
 220     </p>
 221
 222     <p>
 223       <label>
 224         <input type="checkbox" value="">
 225         Check this checkbox
 226       </label>
 227     </p>
 228
 229     <p>
 230       <label>
 231         <input type="radio" name="optionsRadios" id="optionsRadios1" value="option1" checked>
 232         Option one is this and that
 233       </label>
 234       <label>
 235         <input type="radio" name="optionsRadios" id="optionsRadios2" value="option2">
 236         Option two is something else that's also super long to demonstrate the wrapping of these fancy form controls.
 237       </label>
 238       <label>
 239         <input type="radio" name="optionsRadios" id="optionsRadios3" value="option3" disabled>
 240         Option three is disabled
 241       </label>
 242     </p>
 243
 244     <p>
 245       <label for="textarea">Example textarea</label>
 246       <textarea id="textarea" rows="3"></textarea>
 247     </p>
 248
 249     <p>
 250       <label for="time">Example temporal</label>
 251       <input type="datetime-local" id="time">
 252     </p>
 253
 254     <p>
 255       <label for="output">Example output</label>
 256       <output name="result" id="output">100</output>
 257     </p>
 258
 259     <p>
 260       <button type="submit">Button submit</button>
 261       <input type="submit" value="Input submit button">
 262       <input type="button" value="Input button">
 263     </p>
 264
 265     <p>
 266       <button type="submit" disabled>Button submit</button>
 267       <input type="submit" value="Input submit button" disabled>
 268       <input type="button" value="Input button" disabled>
 269     </p>
 270   </fieldset>
 271 </form>
 272
 273 ## Misc elements
 274
 275 ### Address
 276
 277 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>`.
 278
 279 <div class="bd-example">
 280   <address>
 281     <strong>Twitter, Inc.</strong><br>
 282     1355 Market St, Suite 900<br>
 283     San Francisco, CA 94103<br>
 284     <abbr title="Phone">P:</abbr> (123) 456-7890
 285   </address>
 286
 287   <address>
 288     <strong>Full Name</strong><br>
 289     <a href="mailto:#">first.last@example.com</a>
 290   </address>
 291 </div>
 292
 293 ### Blockquote
 294
 295 The default `margin` on blockquotes is `1em 40px`, so we reset that to `0 0 1rem` for something more consistent with other elements.
 296
 297 <div class="bd-example">
 298   <blockquote class="blockquote">
 299     <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
 300     <footer>Someone famous in <cite title="Source Title">Source Title</cite></footer>
 301   </blockquote>
 302 </div>
 303
 304 ### Inline elements
 305
 306 The `<abbr>` element receives basic styling to make it stand out amongst paragraph text.
 307
 308 <div class="bd-example">
 309   Nulla <abbr title="attribute">attr</abbr> vitae elit libero, a pharetra augue.
 310 </div>
 311
 312 ## HTML5 `[hidden]` attribute
 313
 314 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 IE10, the explicit declaration in our CSS gets around that problem.
 315
 316 {% highlight html %}
 317 <input type="text" hidden>
 318 {% endhighlight %}
 319
 320 {% callout warning %}
 321 #### jQuery incompatibility
 322
 323 `[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.
 324 {% endcallout %}
 325
 326 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 }}/utilities/invisible-content/) instead.
 327
 328 ## Click delay optimization for touch
 329
 330 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.
 331
 332 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/).
 333
 334 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.
 335
 336 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.
 337
 338 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.
 339
 340 For further details, see the compatibility table for [suppressing 300ms delay for touchscreen interactions](https://patrickhlauke.github.io/touch/tests/results/#suppressing-300ms-delay).