MessagePractise/resources/scss/vue/bootstrap-vue/_file-input.scss

.b-form-file {
  .custom-file-label {
    height: 100% !important;
  }
  // Small
  &.b-custom-control-sm {
    .custom-file-label,
    .custom-file-label::after {
      line-height: 22px;
    }

    .custom-file-label::after {
      height: 28px;
    }
  }
  // Large
  &.b-custom-control-lg {
    .custom-file-label,
    .custom-file-label::after {
      line-height: 23px;
    }

    .custom-file-label::after {
      height: 44px;
    }
  }
}