SOURCE

<h1>Example heading <span class="badge badge-secondary">New</span></h1>
<h2>Example heading <span class="badge badge-secondary">New</span></h2>
<h3>Example heading <span class="badge badge-secondary">New</span></h3>
<h4>Example heading <span class="badge badge-secondary">New</span></h4>
<h5>Example heading <span class="badge badge-secondary">New</span></h5>
<h6>Example heading <span class="badge badge-secondary">New</span></h6>

<button type="button" class="btn btn-primary">
  Notifications <span class="badge badge-light">4</span>
</button>

<span class="badge badge-primary">Primary</span>
<span class="badge badge-secondary">Secondary</span>
<span class="badge badge-success">Success</span>
<span class="badge badge-danger">Danger</span>
<span class="badge badge-warning">Warning</span>
<span class="badge badge-info">Info</span>
<span class="badge badge-light">Light</span>
<span class="badge badge-dark">Dark</span>
<div></div>
<span class="badge badge-pill badge-primary">Primary</span>
<span class="badge badge-pill badge-secondary">Secondary</span>
<span class="badge badge-pill badge-success">Success</span>
<span class="badge badge-pill badge-danger">Danger</span>
<span class="badge badge-pill badge-warning">Warning</span>
<span class="badge badge-pill badge-info">Info</span>
<span class="badge badge-pill badge-light">Light</span>
<span class="badge badge-pill badge-dark">Dark</span>


<a href="#" class="badge badge-primary">Primary</a>
<a href="#" class="badge badge-secondary">Secondary</a>
<a href="#" class="badge badge-success">Success</a>
<a href="#" class="badge badge-danger">Danger</a>
<a href="#" class="badge badge-warning">Warning</a>
<a href="#" class="badge badge-info">Info</a>
<a href="#" class="badge badge-light">Light</a>
<a href="#" class="badge badge-dark">Dark</a>

// 全局颜色变量
// Variables
//
// Variables should follow the `$component-state-property-size` formula for
// consistent naming. Ex: $nav-link-disabled-color and $modal-content-box-shadow-xs.


//
// Color system
//

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

$grays: () !default;
$grays: map-merge((
  "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
), $grays);

$blue:    #007bff !default;
$indigo:  #6610f2 !default;
$purple:  #6f42c1 !default;
$pink:    #e83e8c !default;
$red:     #dc3545 !default;
$orange:  #fd7e14 !default;
$yellow:  #ffc107 !default;
$green:   #28a745 !default;
$teal:    #20c997 !default;
$cyan:    #17a2b8 !default;

$colors: () !default;
$colors: map-merge((
  "blue":       $blue,
  "indigo":     $indigo,
  "purple":     $purple,
  "pink":       $pink,
  "red":        $red,
  "orange":     $orange,
  "yellow":     $yellow,
  "green":      $green,
  "teal":       $teal,
  "cyan":       $cyan,
  "white":      $white,
  "gray":       $gray-600,
  "gray-dark":  $gray-800
), $colors);

$primary:       $blue !default;
$secondary:     $gray-600 !default;
$success:       $green !default;
$info:          $cyan !default;
$warning:       $yellow !default;
$danger:        $red !default;
$light:         $gray-100 !default;
$dark:          $gray-800 !default;

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

// 工具函数 生成反色
// The yiq lightness value that determines when the lightness of color changes from "dark" to "light". Acceptable values are between 0 and 255.
$yiq-contrasted-threshold: 150 !default;

// Customize the light and dark text colors for use in our YIQ color contrast function.
$yiq-text-dark: $gray-900 !default;
$yiq-text-light: $white !default;
@function color-yiq($color) {
  $r: red($color);
  $g: green($color);
  $b: blue($color);

  $yiq: (($r * 299) + ($g * 587) + ($b * 114)) / 1000;

  @if ($yiq >= $yiq-contrasted-threshold) {
    @return $yiq-text-dark;
  } @else {
    @return $yiq-text-light;
  }
}

$badge-padding-x: .4em;
$badge-padding-y: .25em;
$badge-border-radius: .25rem;

.badge{
  display: inline-block;
  padding: $badge-padding-y $badge-padding-x;
  border-radius: $badge-border-radius;
  font-size: 75%;
  font-weight: 700;
  line-height: 1;
  text-align: center;
  vertical-align: baseline;
  text-decoration: none;
}
.badge-pill{
  border-radius: 10rem;
}
@each $color-name, $color-value in $theme-colors{
  .badge-#{$color-name}{
    background: $color-value;
    color: color-yiq($color-value);
    &[href]:hover, &[href]:focus{
      background: darken($color-value, 10%);
    }
  }
}