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# Utilities for layout

For faster mobile-friendly and responsive development, Bootstrap includes dozens of utility classes for showing, hiding, aligning, and spacing content.

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Changing `display`

Use our display utilities for responsively toggling common values of the `display` property. Mix it with our grid system, content, or components to show or hide them across specific viewports.

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Flexbox options

Bootstrap 4 is built with flexbox, but not every element’s `display` has been changed to `display: flex` as this would add many unnecessary overrides and unexpectedly change key browser behaviors. Most of our components are built with flexbox enabled.

Should you need to add `display: flex` to an element, do so with `.d-flex` or one of the responsive variants (e.g., `.d-sm-flex`). You’ll need this class or `display` value to allow the use of our extra flexbox utilities for sizing, alignment, spacing, and more.

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Margin and padding

Use the `margin` and `padding` spacing utilities to control how elements and components are spaced and sized. Bootstrap 4 includes a five-level scale for spacing utilities, based on a `1rem` value default `$spacer` variable. Choose values for all viewports (e.g., `.mr-3` for `margin-right: 1rem`), or pick responsive variants to target specific viewports (e.g., `.mr-md-3` for `margin-right: 1rem` starting at the `md` breakpoint).

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Toggle `visibility`

When toggling `display` isn’t needed, you can toggle the `visibility` of an element with our visibility utilities. Invisible elements will still affect the layout of the page, but are visually hidden from visitors.