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Adding upstream version 5.2.3+dfsg.

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Signed-off-by: Daniel Baumann <daniel@debian.org>
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---
layout: docs
title: Background
description: Convey meaning through `background-color` and add decoration with gradients.
group: utilities
toc: true
---
## Background color
Similar to the contextual text color classes, set the background of an element to any contextual class. Background utilities **do not set `color`**, so in some cases you'll want to use `.text-*` [color utilities]({{< docsref "/utilities/colors" >}}).
{{< example >}}
{{< colors.inline >}}
{{- range (index $.Site.Data "theme-colors") }}
<div class="p-3 mb-2 bg-{{ .name }}{{ if .contrast_color }} text-{{ .contrast_color }}{{ else }} text-white{{ end }}">.bg-{{ .name }}</div>
{{- end -}}
{{< /colors.inline >}}
<div class="p-3 mb-2 bg-body text-dark">.bg-body</div>
<div class="p-3 mb-2 bg-white text-dark">.bg-white</div>
<div class="p-3 mb-2 bg-transparent text-dark">.bg-transparent</div>
{{< /example >}}
## Background gradient
By adding a `.bg-gradient` class, a linear gradient is added as background image to the backgrounds. This gradient starts with a semi-transparent white which fades out to the bottom.
Do you need a gradient in your custom CSS? Just add `background-image: var(--bs-gradient);`.
{{< markdown >}}
{{< colors.inline >}}
{{- range (index $.Site.Data "theme-colors") }}
<div class="p-3 mb-2 bg-{{ .name }} bg-gradient{{ with .contrast_color }} text-{{ . }}{{ else }} text-white{{ end }}">.bg-{{ .name }}.bg-gradient</div>
{{- end -}}
{{< /colors.inline >}}
{{< /markdown >}}
## Opacity
{{< added-in "5.1.0" >}}
As of v5.1.0, `background-color` utilities are generated with Sass using CSS variables. This allows for real-time color changes without compilation and dynamic alpha transparency changes.
### How it works
Consider our default `.bg-success` utility.
```css
.bg-success {
--bs-bg-opacity: 1;
background-color: rgba(var(--bs-success-rgb), var(--bs-bg-opacity)) !important;
}
```
We use an RGB version of our `--bs-success` (with the value of `25, 135, 84`) CSS variable and attached a second CSS variable, `--bs-bg-opacity`, for the alpha transparency (with a default value `1` thanks to a local CSS variable). That means anytime you use `.bg-success` now, your computed `color` value is `rgba(25, 135, 84, 1)`. The local CSS variable inside each `.bg-*` class avoids inheritance issues so nested instances of the utilities don't automatically have a modified alpha transparency.
### Example
To change that opacity, override `--bs-bg-opacity` via custom styles or inline styles.
{{< example >}}
<div class="bg-success p-2 text-white">This is default success background</div>
<div class="bg-success p-2" style="--bs-bg-opacity: .5;">This is 50% opacity success background</div>
{{< /example >}}
Or, choose from any of the `.bg-opacity` utilities:
{{< example >}}
<div class="bg-success p-2 text-white">This is default success background</div>
<div class="bg-success p-2 text-white bg-opacity-75">This is 75% opacity success background</div>
<div class="bg-success p-2 text-dark bg-opacity-50">This is 50% opacity success background</div>
<div class="bg-success p-2 text-dark bg-opacity-25">This is 25% opacity success background</div>
<div class="bg-success p-2 text-dark bg-opacity-10">This is 10% opacity success background</div>
{{< /example >}}
## Sass
In addition to the following Sass functionality, consider reading about our included [CSS custom properties]({{< docsref "/customize/css-variables" >}}) (aka CSS variables) for colors and more.
### Variables
Most `background-color` utilities are generated by our theme colors, reassigned from our generic color palette variables.
{{< scss-docs name="color-variables" file="scss/_variables.scss" >}}
{{< scss-docs name="theme-color-variables" file="scss/_variables.scss" >}}
{{< scss-docs name="variable-gradient" file="scss/_variables.scss" >}}
Grayscale colors are also available, but only a subset are used to generate any utilities.
{{< scss-docs name="gray-color-variables" file="scss/_variables.scss" >}}
### Map
Theme colors are then put into a Sass map so we can loop over them to generate our utilities, component modifiers, and more.
{{< scss-docs name="theme-colors-map" file="scss/_variables.scss" >}}
Grayscale colors are also available as a Sass map. **This map is not used to generate any utilities.**
{{< scss-docs name="gray-colors-map" file="scss/_variables.scss" >}}
RGB colors are generated from a separate Sass map:
{{< scss-docs name="theme-colors-rgb" file="scss/_maps.scss" >}}
And background color opacities build on that with their own map that's consumed by the utilities API:
{{< scss-docs name="utilities-bg-colors" file="scss/_maps.scss" >}}
### Mixins
**No mixins are used to generate our background utilities**, but we do have some additional mixins for other situations where you'd like to create your own gradients.
{{< scss-docs name="gradient-bg-mixin" file="scss/mixins/_gradients.scss" >}}
{{< scss-docs name="gradient-mixins" file="scss/mixins/_gradients.scss" >}}
### Utilities API
Background utilities are declared in our utilities API in `scss/_utilities.scss`. [Learn how to use the utilities API.]({{< docsref "/utilities/api#using-the-api" >}})
{{< scss-docs name="utils-bg-color" file="scss/_utilities.scss" >}}