introduce a default render implementation on the base widget, which add_media and then call the newly introduced method _render(form, field, formrenderer), abstract of the base widget class. This allow a litle code factorisation and avoid to forget the call to add_media in subclasses.

/* specific workarounds for Internet Explorer */
div.calpopup {
  margin-left: 0px;
  margin-top: 0px;
}

/* quick and dirty solution for pop to be 
   correctly displayed on right edge of window */
div.popupWrapper{ 
  direction:rtl;
}