description: 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.
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 `rem`s instead of `em`s 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 `rem`s for `margin`s.
- Keep declarations of `font`-related properties to a minimum, using `inherit` whenever possible.
## 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.
- The `<body>` also sets a global `font-family`, `line-height`, and `text-align`. This is inherited later by some form elements to prevent font inconsistencies.
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/).
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.
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.
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**.
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 }}/docs/{{ site.docs_version }}/content/tables/).
-`<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.
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>`.
<divclass="bd-example">
<address>
<strong>Twitter, Inc.</strong><br>
1355 Market St, Suite 900<br>
San Francisco, CA 94103<br>
<abbrtitle="Phone">P:</abbr> (123) 456-7890
</address>
<address>
<strong>Full Name</strong><br>
<ahref="mailto:#">first.last@example.com</a>
</address>
</div>
### Blockquote
The default `margin` on blockquotes is `1em 40px`, so we reset that to `0 0 1rem` for something more consistent with other elements.
<divclass="bd-example">
<blockquoteclass="blockquote">
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
<footer>Someone famous in <citetitle="Source Title">Source Title</cite></footer>
</blockquote>
</div>
### Inline elements
The `<abbr>` element receives basic styling to make it stand out amongst paragraph text.
<divclass="bd-example">
Nulla <abbrtitle="attribute">attr</abbr> vitae elit libero, a pharetra augue.
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](https://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.
`[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.
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 }}/docs/{{ site.docs_version }}/utilities/visibility/) instead.
