Bootstrap/less/mixins/progress-bar.less

// Progress bars

.progress-variant(@color) {
  &[value]::-webkit-progress-value {
    background-color: @color;
  }
  &[value]::-moz-progress-bar {
    background-color: @color;
  }
  @media screen and (~"min-width:0\0") {
    .progress-bar {
      background-color: @color;
    }
  }
}