Background

通过background-color传达意义，以及添加渐变装饰。

On this page

**无障碍可访问性提示：**使用颜色来增加意义只提供了一种视觉指示，而不会传达给屏幕阅读器等辅助技术的用户。请确保其含义从内容本身来看是显而易见的(例如，具有足够颜色对比度)，或者通过其他方式包含，例如使用.visually-hidden类隐藏的其他文本。

背景颜色

与上下文文本颜色类类似，将元素的背景设置为任何上下文类。 Background utilities 不会设置文本color，因此在某些情况下，你需要使用.text-* color Utility。

Background utilities，如从我们的原始 $theme-colors Sass Map生成的 .bg-*-subtle，还没有对颜色模式做出响应，然而，任何.bg-*-inquiet Utility都会做出响应。这将在v6中解决。

.bg-primary

.bg-primary-subtle

.bg-secondary

.bg-secondary-subtle

.bg-success

.bg-success-subtle

.bg-danger

.bg-danger-subtle

.bg-warning

.bg-warning-subtle

.bg-info

.bg-info-subtle

.bg-light

.bg-light-subtle

.bg-dark

.bg-dark-subtle

.bg-body-secondary

.bg-body-tertiary

.bg-body

.bg-black

.bg-white

.bg-transparent

html

<div class="p-3 mb-2 bg-primary text-white">.bg-primary</div>
<div class="p-3 mb-2 bg-primary-subtle text-primary-emphasis">.bg-primary-subtle</div>
<div class="p-3 mb-2 bg-secondary text-white">.bg-secondary</div>
<div class="p-3 mb-2 bg-secondary-subtle text-secondary-emphasis">.bg-secondary-subtle</div>
<div class="p-3 mb-2 bg-success text-white">.bg-success</div>
<div class="p-3 mb-2 bg-success-subtle text-success-emphasis">.bg-success-subtle</div>
<div class="p-3 mb-2 bg-danger text-white">.bg-danger</div>
<div class="p-3 mb-2 bg-danger-subtle text-danger-emphasis">.bg-danger-subtle</div>
<div class="p-3 mb-2 bg-warning text-dark">.bg-warning</div>
<div class="p-3 mb-2 bg-warning-subtle text-warning-emphasis">.bg-warning-subtle</div>
<div class="p-3 mb-2 bg-info text-dark">.bg-info</div>
<div class="p-3 mb-2 bg-info-subtle text-info-emphasis">.bg-info-subtle</div>
<div class="p-3 mb-2 bg-light text-dark">.bg-light</div>
<div class="p-3 mb-2 bg-light-subtle text-light-emphasis">.bg-light-subtle</div>
<div class="p-3 mb-2 bg-dark text-white">.bg-dark</div>
<div class="p-3 mb-2 bg-dark-subtle text-dark-emphasis">.bg-dark-subtle</div>
<p class="p-3 mb-2 bg-body-secondary">.bg-body-secondary</p>
<p class="p-3 mb-2 bg-body-tertiary">.bg-body-tertiary</p>

<div class="p-3 mb-2 bg-body text-body">.bg-body</div>
<div class="p-3 mb-2 bg-black text-white">.bg-black</div>
<div class="p-3 mb-2 bg-white text-dark">.bg-white</div>
<div class="p-3 mb-2 bg-transparent text-body">.bg-transparent</div>

背景渐变

通过添加 .bg-gradient 类，将线性梯度作为背景图像添加到背景中。此渐变从半透明的白色开始，白色逐渐淡出到底部。

你的自定义CSS需要渐变吗？只需添加 background-image: var(--bs-gradient);。

.bg-primary.bg-gradient

.bg-secondary.bg-gradient

.bg-success.bg-gradient

.bg-danger.bg-gradient

.bg-warning.bg-gradient

.bg-info.bg-gradient

.bg-light.bg-gradient

.bg-dark.bg-gradient

.bg-black.bg-gradient

不透明度

Added in v5.1.0

从v5.1.0开始，background-color Utility是使用CSS变量通过Sass生成的。这允许在没有编译和动态alpha透明度更改的情况下实时更改颜色。

它是如何工作的

请考虑我们的默认 .bg-success Utility。

.bg-success {
  --bs-bg-opacity: 1;
  background-color: rgba(var(--bs-success-rgb), var(--bs-bg-opacity)) !important;
}

我们使用RGB版本的 --bs-success (值为25, 135, 84)CSS变量，并附加第二个CSS变量 --bs-bg-opacity作为alpha透明度(由于本地CSS变量，默认值为1)。这意味着，无论何时你现在使用.bg-success，你计算的color值都是rgba(25, 135, 84, 1)。每个.bg-*类中的本地CSS变量避免了继承问题，因此 Utility的嵌套实例不会自动具有修改后的alpha透明度。

实例

若要更改不透明度，请通过自定义样式或内联样式覆盖--bs-bg-opacity。

This is default success background

This is 50% opacity success background

html

<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>

或者，从任何.bg-opacity Utility中进行选择：

This is default success background

This is 75% opacity success background

This is 50% opacity success background

This is 25% opacity success background

This is 10% opacity success background

html

<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>

CSS

除了以下Sass功能外，还可以考虑阅读我们包含的CSS自定义属性也称为CSS变量）中的颜色和其他内容。

Sass变量

大多数 background-color Utility都是由我们的主题颜色生成的，这些颜色是从我们的通用调色板变量中重新分配的。

scss/_variables.scss

$blue:    #0d6efd;
$indigo:  #6610f2;
$purple:  #6f42c1;
$pink:    #d63384;
$red:     #dc3545;
$orange:  #fd7e14;
$yellow:  #ffc107;
$green:   #198754;
$teal:    #20c997;
$cyan:    #0dcaf0;

scss/_variables.scss

$primary:       $blue;
$secondary:     $gray-600;
$success:       $green;
$info:          $cyan;
$warning:       $yellow;
$danger:        $red;
$light:         $gray-100;
$dark:          $gray-900;

scss/_variables.scss

$gradient: linear-gradient(180deg, rgba($white, .15), rgba($white, 0));

灰度颜色也可用，但只有一个子集用于生成任何 Utility。

scss/_variables.scss

$white:    #fff;
$gray-100: #f8f9fa;
$gray-200: #e9ecef;
$gray-300: #dee2e6;
$gray-400: #ced4da;
$gray-500: #adb5bd;
$gray-600: #6c757d;
$gray-700: #495057;
$gray-800: #343a40;
$gray-900: #212529;
$black:    #000;

在明暗模式下，用于在 .bg-*-subtle utilities 中设置background-color 的变量：

scss/_variables.scss

$primary-bg-subtle:       tint-color($primary, 80%);
$secondary-bg-subtle:     tint-color($secondary, 80%);
$success-bg-subtle:       tint-color($success, 80%);
$info-bg-subtle:          tint-color($info, 80%);
$warning-bg-subtle:       tint-color($warning, 80%);
$danger-bg-subtle:        tint-color($danger, 80%);
$light-bg-subtle:         mix($gray-100, $white);
$dark-bg-subtle:          $gray-400;

scss/_variables-dark.scss

$primary-bg-subtle-dark:            shade-color($primary, 80%);
$secondary-bg-subtle-dark:          shade-color($secondary, 80%);
$success-bg-subtle-dark:            shade-color($success, 80%);
$info-bg-subtle-dark:               shade-color($info, 80%);
$warning-bg-subtle-dark:            shade-color($warning, 80%);
$danger-bg-subtle-dark:             shade-color($danger, 80%);
$light-bg-subtle-dark:              $gray-800;
$dark-bg-subtle-dark:               mix($gray-800, $black);

Sass maps

然后将主题颜色放入Sass Map中，这样我们就可以循环使用它们来生成我们的 Utility、组件修饰符等。

scss/_variables.scss

$theme-colors: (
  "primary":    $primary,
  "secondary":  $secondary,
  "success":    $success,
  "info":       $info,
  "warning":    $warning,
  "danger":     $danger,
  "light":      $light,
  "dark":       $dark
);

灰度颜色也可用作Sass Map。 此 Map 不用于生成任何 Utility

scss/_variables.scss

$grays: (
  "100": $gray-100,
  "200": $gray-200,
  "300": $gray-300,
  "400": $gray-400,
  "500": $gray-500,
  "600": $gray-600,
  "700": $gray-700,
  "800": $gray-800,
  "900": $gray-900
);

RGB颜色由单独的Sass Map生成：

scss/_maps.scss

$theme-colors-rgb: map-loop($theme-colors, to-rgb, "$value");

背景颜色不透明性建立在它们自己的 Map 上，这些贴图由 UtilityAPI使用：

scss/_maps.scss

$utilities-bg: map-merge(
  $utilities-colors,
  (
    "black": to-rgb($black),
    "white": to-rgb($white),
    "body": to-rgb($body-bg)
  )
);
$utilities-bg-colors: map-loop($utilities-bg, rgba-css-var, "$key", "bg");

$utilities-bg-subtle: (
  "primary-subtle": var(--#{$prefix}primary-bg-subtle),
  "secondary-subtle": var(--#{$prefix}secondary-bg-subtle),
  "success-subtle": var(--#{$prefix}success-bg-subtle),
  "info-subtle": var(--#{$prefix}info-bg-subtle),
  "warning-subtle": var(--#{$prefix}warning-bg-subtle),
  "danger-subtle": var(--#{$prefix}danger-bg-subtle),
  "light-subtle": var(--#{$prefix}light-bg-subtle),
  "dark-subtle": var(--#{$prefix}dark-bg-subtle)
);

颜色模式背景颜色也可用Sass Map实现：

scss/_maps.scss

$theme-colors-bg-subtle: (
  "primary": $primary-bg-subtle,
  "secondary": $secondary-bg-subtle,
  "success": $success-bg-subtle,
  "info": $info-bg-subtle,
  "warning": $warning-bg-subtle,
  "danger": $danger-bg-subtle,
  "light": $light-bg-subtle,
  "dark": $dark-bg-subtle,
);

scss/_maps.scss

$theme-colors-bg-subtle-dark: (
  "primary": $primary-bg-subtle-dark,
  "secondary": $secondary-bg-subtle-dark,
  "success": $success-bg-subtle-dark,
  "info": $info-bg-subtle-dark,
  "warning": $warning-bg-subtle-dark,
  "danger": $danger-bg-subtle-dark,
  "light": $light-bg-subtle-dark,
  "dark": $dark-bg-subtle-dark,
);

Sass mixins

没有mixin来生成我们的背景 Utility，但我们确实有一些额外的mixin，用于你想要创建自己的渐变的其他情况。

scss/mixins/_gradients.scss

@mixin gradient-bg($color: null) {
  background-color: $color;

  @if $enable-gradients {
    background-image: var(--#{$prefix}gradient);
  }
}

scss/mixins/_gradients.scss

// Horizontal gradient, from left to right
//
// Creates two color stops, start and end, by specifying a color and position for each color stop.
@mixin gradient-x($start-color: $gray-700, $end-color: $gray-800, $start-percent: 0%, $end-percent: 100%) {
  background-image: linear-gradient(to right, $start-color $start-percent, $end-color $end-percent);
}

// Vertical gradient, from top to bottom
//
// Creates two color stops, start and end, by specifying a color and position for each color stop.
@mixin gradient-y($start-color: $gray-700, $end-color: $gray-800, $start-percent: null, $end-percent: null) {
  background-image: linear-gradient(to bottom, $start-color $start-percent, $end-color $end-percent);
}

@mixin gradient-directional($start-color: $gray-700, $end-color: $gray-800, $deg: 45deg) {
  background-image: linear-gradient($deg, $start-color, $end-color);
}

@mixin gradient-x-three-colors($start-color: $blue, $mid-color: $purple, $color-stop: 50%, $end-color: $red) {
  background-image: linear-gradient(to right, $start-color, $mid-color $color-stop, $end-color);
}

@mixin gradient-y-three-colors($start-color: $blue, $mid-color: $purple, $color-stop: 50%, $end-color: $red) {
  background-image: linear-gradient($start-color, $mid-color $color-stop, $end-color);
}

@mixin gradient-radial($inner-color: $gray-700, $outer-color: $gray-800) {
  background-image: radial-gradient(circle, $inner-color, $outer-color);
}

@mixin gradient-striped($color: rgba($white, .15), $angle: 45deg) {
  background-image: linear-gradient($angle, $color 25%, transparent 25%, transparent 50%, $color 50%, $color 75%, transparent 75%, transparent);
}

Sass UtilityAPI

Background Utility在我们的 Utility API中声明为scss/_utilities.scss。了解如何使用 UtilityAPI。

scss/_utilities.scss

"background-color": (
  property: background-color,
  class: bg,
  local-vars: (
    "bg-opacity": 1
  ),
  values: map-merge(
    $utilities-bg-colors,
    (
      "transparent": transparent,
      "body-secondary": rgba(var(--#{$prefix}secondary-bg-rgb), var(--#{$prefix}bg-opacity)),
      "body-tertiary": rgba(var(--#{$prefix}tertiary-bg-rgb), var(--#{$prefix}bg-opacity)),
    )
  )
),
"bg-opacity": (
  css-var: true,
  class: bg-opacity,
  values: (
    10: .1,
    25: .25,
    50: .5,
    75: .75,
    100: 1
  )
),
"subtle-background-color": (
  property: background-color,
  class: bg,
  values: $utilities-bg-subtle
),