webpack-bootstrap-ui-kit/src/scss/layout/main/alerts.scss

#SiteWideAlerts {
  bottom: 0;
  position: fixed;
  right: 0;
  z-index: 99999;

  .btn-close {
    background: none;
  }

  .alert {
    margin-bottom: 0;
  }
}

.alert-offline {
  display: none;
}

.is-online {
  .alert-offline {
    display: none;
  }
}

.is-offline {
  .alert-offline {
    display: flex;
  }
}