fix compile for bootstra 4.5.3

[roojs1] / scss / bootstrap / mixins / _badge.scss

@mixin badge-variant($bg) {
  color: color-yiq($bg);
  background-color: $bg;

  /* @at-root a#{&} { */
  &[href] {
    @include hover-focus() {
      color: color-yiq($bg);
      background-color: darken($bg, 10%);
    }

    &:focus,
    &.focus {
      outline: 0;
      box-shadow: 0 0 0 $badge-focus-width rgba($bg, .5);
    }
  }
}