背景

通过背景颜色background-color传达意义并用渐变添加装饰。

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背景颜色

类似于上下文文本颜色类，将元素的背景设置为任何上下文类。后台实用程序没有设置color，所以在某些情况下您会想要使用.text-* 颜色实用程序。

.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-emphasis-primary">.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-emphasis-secondary">.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-emphasis-success">.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-emphasis-danger">.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-emphasis-warning">.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-emphasis-info">.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-emphasis-light">.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-emphasis-dark">.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

通过添加一个.bg-gradient类，将线性渐变作为背景图像添加到背景中。这个渐变以半透明的白色开始，逐渐淡出到底部。

您的自定义 CSS 中需要渐变吗？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

添加于 v5.1.0

从 v5.1.0 开始，background-color实用程序是使用 CSS 变量通过 Sass 生成的。这允许实时颜色更改而无需编译和动态 alpha 透明度更改。

怎么运行的

考虑我们的默认.bg-success实用程序。

.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CSS 变量--bs-success（值为25, 135, 84）并附加第二个 CSS 变量，--bs-bg-opacity用于 alpha 透明度（具有默认值1，这要归功于本地 CSS 变量）。这意味着您.bg-success现在使用的任何时候，您的计算color值都是rgba(25, 135, 84, 1)。每个.bg-*类中的局部 CSS 变量避免了继承问题，因此实用程序的嵌套实例不会自动具有修改后的 alpha 透明度。

例子

要更改该不透明度，请--bs-bg-opacity通过自定义样式或内联样式进行覆盖。

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实用程序中进行选择：

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>

Saas

除了以下 Sass 功能之外，请考虑阅读我们包含的颜色等CSS 自定义属性（也称为 CSS 变量）。

变量

大多数background-color实用程序都是由我们的主题颜色生成的，从我们的通用调色板变量中重新分配。

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

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

$gradient: linear-gradient(180deg, rgba($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实用程序。

$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;

映射

然后将主题颜色放入 Sass 映射中，以便我们可以遍历它们以生成我们的实用程序、组件修改器等。

$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 映射。该映射不用于生成任何实用程序。

$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 颜色是从单独的 Sass 映射生成的：

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

背景颜色不透明度建立在它们自己的映射之上，由实用程序 API 使用：

$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)
);
// $utilities-bg-subtle-colors: map-loop($utilities-bg-subtle, rgba-css-var, "$key", "bg");

mixins

没有 mixins 用于生成我们的后台实用程序，但我们确实有一些额外的 mixins 用于您想要创建自己的渐变的其他情况。

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

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

// 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);
}

实用程序接口

后台实用程序在我们的实用程序 API 中声明scss/_utilities.scss。了解如何使用实用程序 API。

    "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(--#{$prefix}bg-opacity)),
          "body-emphasis": rgba(var(--#{$prefix}emphasis-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
    ),