portainer/app/agent/components/file-uploader/file-uploader.html

<button 
  ngf-select="$ctrl.onFileSelected($file)"
  class="btn ng-scope"
  button-spinner="$ctrl.state.uploadInProgress">
  <i style="margin:0" class="fa fa-upload" ng-if="!$ctrl.state.uploadInProgress"></i>
</button>