# Bootstrap 5 Reboot > Reboot, a collection of element-specific CSS changes in a single file, kickstart CoreUI for Bootstrap to provide an elegant, consistent, and simple baseline to build upon. ## Approach 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. 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. ## CSS variables _Added in 4.1.0._ With v4.1.0, we standardized our required `@import`s across all our CSS bundles (including `coreui.css`, `coreui-reboot.css`, and `coreui-grid.css` to include `_root.scss` . This adds `:root` level CSS variables to all bundles, regardless of how many of them are used in that bundle. Ultimately CoreUI will continue to see more CSS variables added over time. ## 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. - No base `font-size` is declared on the ``, but `16px` is assumed (the browser default). `font-size: 1rem` is applied on the `` for easy responsive type-scaling via media queries while respecting user preferences and ensuring a more accessible approach. This browser default can be overridden by modifying the `$font-size-root` variable. - The `` also sets a global `font-family`, `font-weight`, `line-height`, and `color`. This is inherited later by some form elements to prevent font inconsistencies. - For safety, the `` has a declared `background-color`, defaulting to `#fff`. ## Native font stack CoreUI for Bootstrap utilizes a "native font stack" or "system font stack" for optimum text rendering on every device and OS. These system fonts have been designed specifically with today's devices in mind, with improved rendering on screens, variable font support, and more. Read more about [native font stacks in this *Smashing Magazine* article](https://www.smashingmagazine.com/2015/11/using-system-ui-fonts-practical-guide/). ```scss $font-family-sans-serif: // Cross-platform generic font family (default user interface font) system-ui, // Safari for macOS and iOS (San Francisco) -apple-system, // Windows "Segoe UI", // Android Roboto, // older macOS and iOS "Helvetica Neue" // Linux "Noto Sans", "Liberation Sans", // Basic web fallback Arial, // Sans serif fallback sans-serif, // Emoji fonts "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji" !default; ``` Note that because the font stack includes emoji fonts, many common symbol/dingbat unicode characters will be rendered as multi-colored pictographs. Their appearance will vary, depending on the style used in the browser/platform's native emoji font, and they won't be affected by any CSS `color` styles. This `font-family` is applied to the `` and automatically inherited globally throughout Bootstrap. To switch the global `font-family`, update `$font-family-base` and recompile Bootstrap. ## 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. | Heading | Example | | --- | --- | | `

` | h1. Bootstrap heading | | `

` | h2. Bootstrap heading | | `

` | h3. Bootstrap heading | | `

` | h4. Bootstrap heading | | `

` | h5. Bootstrap heading | | `

` | h6. Bootstrap heading | ## Horizontal rules The `

` element has been simplified. Similar to browser defaults, `

`s are styled via `border-top`, have a default `opacity: .25`, and automatically inherit their `border-color` via `color`, including when `color` is set via the parent. They can be modified with text, border, and opacity utilities. ```html

``` ## Lists All lists—`

`s reset `margin-left` to `0` and add `margin-bottom: .5rem`. `
`s are **bolded**. ## Inline code Wrap inline snippets of code with ``. Be sure to escape HTML angle brackets. ```html For example, <section> should be wrapped as inline. ``` ## Code blocks Use ``s for multiple lines of code. Once again, be sure to escape any angle brackets in the code for proper rendering. The `` element is reset to remove its `margin-top` and use `rem` units for its `margin-bottom`. ```html <p>Sample text here...</p> <p>And another line of sample text here...</p> ``` ## Variables For indicating variables use the `` tag. ```html y = mx + b ``` ## User input Use the `` to indicate input that is typically entered via keyboard. ```html To switch directories, type cd followed by the name of the directory. To edit settings, press ctrl + , ``` ## Sample output For indicating sample output from a program use the `` tag. ```html This text is meant to be treated as sample output from a computer program. ``` ## Tables Tables are slightly adjusted to style `

`s, collapse borders, and ensure consistent `text-align` throughout. Additional changes for borders, padding, and more come with [the `.table` class](https://coreui.io/bootstrap/docs/content/tables/). ```html

This is an example table, and this is its 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, and `<button>`s are mostly addressed by Normalize, but Reboot removes their `margin` and sets `line-height: inherit`, too.
- `<textarea>`s are modified to only be resizable vertically as horizontal resizing often "breaks" page layout.
- `<button>`s and `<input />` button elements have `cursor: pointer` when `:not(:disabled)`.

These changes, and more, are demonstrated below.

> ##### Date & color input support
> 
> Keep in mind date inputs are [not fully supported](https://caniuse.com/input-datetime) by all browsers, namely Safari.

### Pointers on buttons

Reboot includes an enhancement for `role="button"` to change the default cursor to `pointer`. Add this attribute to elements to help indicate elements are interactive. This role isn't necessary for `<button>` elements, which get their own `cursor` change.

```html
<span role="button" tabindex="0">Non-button element button</span>
```

## Misc elements

### Address

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 />`.

### Blockquote

The default `margin` on blockquotes is `1em 40px`, so we reset that to `0 0 1rem` for something more consistent with other elements.

### Inline elements

The `<abbr>` element receives basic styling to make it stand out amongst paragraph text.

### Summary

The default `cursor` on summary is `text`, so we reset that to `pointer` to convey that the element can be interacted with by clicking on it.

## HTML5 `[hidden]` attribute

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.

```html
<input type="text" hidden>
```

> ##### jQuery incompatibility
> 
> `[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](https://coreui.io/bootstrap/docs/utilities/visibility/) instead.

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

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