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.
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.
- 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.
- 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.
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.
<divclass="bd-example">
{% 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 %}
</div>
## Lists
All lists—`<ul>`, `<ol>`, and `<dl>`—have their `margin-top` removed and a `margin-bottom: 1rem`. Nested lists have no `margin-bottom`.
<divclass="bd-example">
{% markdown %}
* Lorem ipsum dolor sit amet
* Consectetur adipiscing elit
* Integer molestie lorem at massa
* Facilisis in pretium nisl aliquet
* Nulla volutpat aliquam velit
* Phasellus iaculis neque
* Purus sodales ultricies
* Vestibulum laoreet porttitor sem
* Ac tristique libero volutpat at
* Faucibus porta lacus fringilla vel
* Aenean sit amet erat nunc
* Eget porttitor lorem
1. Lorem ipsum dolor sit amet
2. Consectetur adipiscing elit
3. Integer molestie lorem at massa
4. Facilisis in pretium nisl aliquet
5. Nulla volutpat aliquam velit
6. Faucibus porta lacus fringilla vel
7. Aenean sit amet erat nunc
8. Eget porttitor lorem
{% endmarkdown %}
</div>
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**.
<divclass="bd-example">
{% markdown %}
<dl>
<dt>Description lists</dt>
<dd>A description list is perfect for defining terms.</dd>
<dt>Euismod</dt>
<dd>Vestibulum id ligula porta felis euismod semper eget lacinia odio sem.</dd>
<dd>Donec id elit non mi porta gravida at eget metus.</dd>
<dt>Malesuada porta</dt>
<dd>Etiam porta sem malesuada magna mollis euismod.</dd>
Tables are slightly adjusted to style `<caption>`s and ensure consistent `text-align` throughout. Additional changes for borders, padding, and more come with [the `.table` class]({{ site.baseurl }}/content/tables/).
-`<label>`s are set to `display: inline-block` to allow `margin` to be applied.
-`<input>`s, `<selects>`s, `<textareas>`s, and `<buttons>`s are mostly addressed by Normalize, but Reboot removes their `margin` and sets `line-height: inherit`, too.
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>`.
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.
{% highlight html %}
<inputtype="text"hidden>
{% endhighlight %}
{% callout warning %}
#### jQuery incompatibility
`[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.
{% endcallout %}
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.