Bootstrap CSS class .form-control-file

<input type="file" class="form-control-file" id="exampleFormControlFile1">

/* _forms.scss:71 */
.form-control-file {
  .was-validated &:#{$state},
  &.is-#{$state} {
    ~ .#{$state}-feedback,
    ~ .#{$state}-tooltip {
      display: block;
    }
  }
}