--- layout: page title: Reboot --- All of Bootstrap's element-specific CSS changes are part of what we call the Reboot, a single CSS file of simple overrides. 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 `` styles for a simpler baseline and later provide `.table`, `.table-bordered`, and more. ## Approach Here are our guidelines and reasons for choosing what to override in Reboot: - Use `rem`s and `em`s for units, nothing else. - 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 `rem`s for `margin`s. - Keep declarations of `font`-related properties to a minimal, using `inherit` whenever possible. ## Page defaults The `` and `` 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. - A base `font-size: 16px` is declared on the `` and `font-size: 1rem` on the `` for easy responsive type-scaling via media queryies. - The `` also sets a global `font-family` and `line-height`. This is inherited later by some form elements to prevent font inconsistencies. - For safety, the `` has a declared `background-color`, defaulting to `#fff`. ## Headings and paragraphs All heading elements—e.g., `

`—and `

` are reset to have their `margin-top` removed. Headings have `margin-bottom: .5rem` added and paragraphs `margin-bottom: 1rem` for easy spacing.

{% markdown %} # h1 heading Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum. ## h2 heading Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum. ### h3 heading Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum. #### h4 heading Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum. ##### h5 heading Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum. ###### h6 heading Curabitur blandit tempus porttitor. Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum. {% endmarkdown %}

## Lists All lists—`

`s reset `margin-left` to `0` and add `margin-bottom: .5rem`. `
`s are **bolded**.
{% markdown %}

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.

{% endmarkdown %}
## Preformatted text The `
` element is reset to remove its `margin-top` and use `rem` units for its `margin-bottom`.
{% markdown %}
.element { margin-bottom: 1rem; }
{% endmarkdown %}
## Tables Tables are slightly adjusted to style `

`s and ensure consistent `text-align` throughout.

This is an example table, and this is it's 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: - `

`s have no borders, padding, or margin so they can be easily used as wrappers for individual inputs or groups of inputs. = ``s, like fieldsets, have also been restyled to be displayed as a heading of sorts. - ``s are set to `display: inline-block` to allow `margin` to be applied. - ``s, ``s, ``s, and ``s are mostly addressed by Normalize, but Reboot removes their `margin` and sets `line-height: inherit`, too. - `

`s are modified to only be resizeble vertically as horizontal resizing often "breaks" page layout.

These changes, and more, are demonstrated below.

<form class="bd-example">
  <fieldset>
    <legend>Example legend</legend>

<p>
      <label for="input">Example input</label>
      <input type="text" id="input" placeholder="Example input">
    </p>

<p>
      <label for="select">Example select</label>
      <select id="select">
        <option value="">Choose...</option>
        <optgroup label="Option group 1">
          <option value="">Option 1</option>
          <option value="">Option 2</option>
          <option value="">Option 3</option>
        </optgroup>
        <optgroup label="Option group 2">
          <option value="">Option 4</option>
          <option value="">Option 5</option>
          <option value="">Option 6</option>
        </optgroup>
      </select>
    </p>

<p>
      <label>
        <input type="checkbox" value="">
        Check this checkbox
      </label>
    </p>

<p>
      <label>
        <input type="radio" name="optionsRadios" id="optionsRadios1" value="option1" checked>
        Option one is this and that
      </label>
      <label>
        <input type="radio" name="optionsRadios" id="optionsRadios2" value="option2">
        Option two is something else that's also super long to demonstrate the wrapping of these fancy form controls.
      </label>
      <label>
        <input type="radio" name="optionsRadios" id="optionsRadios3" value="option3" disabled>
        Option three is disabled
      </label>
    </p>

<p>
      <label for="textarea">Example textarea</label>
      <textarea id="example" rows="3">

Example temporal

Example output 100

## Misc elements ### Address The `

` 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.

Twitter, Inc.
795 Folsom Ave, Suite 600
San Francisco, CA 94107
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.

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.

Someone famous in Source Title

### Inline elements The `` element receives basic styling to make it stand the amongst paragraph text.

Nulla attr vitae elit libero, a pharetra augue.