Bootstrap class: .custom-radio

<div class="custom-control custom-radio">
  <input type="radio" id="customRadio1" name="customRadio" class="custom-control-input">
  <label class="custom-control-label" for="customRadio1">Toggle this custom radio</label>
</div>
<div class="custom-control custom-radio">
  <input type="radio" id="customRadio2" name="customRadio" class="custom-control-input">
  <label class="custom-control-label" for="customRadio2">Or toggle this other custom radio</label>
</div>

Preview

Toggle this custom radio

Or toggle this other custom radio

Sass source

/* _custom-forms.scss:136 */
.custom-radio {
  .custom-control-label::before {
    border-radius: $custom-radio-indicator-border-radius;
  }

  .custom-control-input:checked ~ .custom-control-label {
    &::before {
      @include gradient-bg($custom-control-indicator-checked-bg);
    }
    &::after {
      background-image: $custom-radio-indicator-icon-checked;
    }
  }

  .custom-control-input:disabled {
    &:checked ~ .custom-control-label::before {
      background-color: $custom-control-indicator-checked-disabled-bg;
    }
  }
}

Uses variables

/* _custom-forms.scss:136 */
$custom-radio-indicator-border-radius
$custom-control-indicator-checked-bg
$custom-radio-indicator-icon-checked
$custom-control-indicator-checked-disabled-bg