Comment 10 for bug 1437173

Maybe I have solved this problem. Make some changes and let's see what happened.

File: /usr/share/themes/elementary/gtk-3.0/gtk.css

/* Add this line to end of the file */
@define-color backdrop_bg_color @theme_bg_color;

File: /usr/share/themes/elementary/gtk-3.0/gtk-widgets.css
search for '.window-frame { .... }' replace the whole block by following code

.window-frame {
  border-radius: 5px 5px 0 0;
  border-width: 0;
  box-shadow: 0 3px 9px 1px rgba(0, 0, 0, 0.5), 0 0 0 1px rgba(0, 0, 0, 0.23);
  margin: 10px; }
  .window-frame:backdrop {
    box-shadow: 0 1px 6px 2px rgba(0, 0, 0, 0.2), 0 0 0 1px rgba(0, 0, 0, 0.18); }
  .window-frame.tiled {
    border-radius: 0; }
  .window-frame.csd.popup {
    border-radius: 0;
    box-shadow: 0 1px 2px rgba(0, 0, 0, 0.2), 0 0 0 1px rgba(0, 0, 0, 0.13); }

/* classic decoration */
  .window-frame.ssd {
    border-radius: 5px 5px 0 0;
    box-shadow: 0 0 0 1px rgba(0, 0, 0, 0.18); }
  .window-frame.ssd,
  .window-frame.ssd:backdrop {
    background-color: @backdrop_bg_color}

  .window-frame.csd.tooltip {
    border-radius: 0;
    box-shadow: none; }
  .window-frame.csd.message-dialog {
    border-radius: 3px;
    box-shadow: 0 1px 2px rgba(0, 0, 0, 0.2), 0 0 0 1px rgba(0, 0, 0, 0.13); }
 .window-frame.solid-csd {
     border: solid 1px shade(@bg_color, 0.8);
     border-radius: 0;
     margin: 2px;
     background-color: @bg_color;
     box-shadow: none;
}

Save and logout. In my case it solved shadow issue. I installed elementary-desktop over Ubuntu. Can anybody please check it for fresh installed elementary Loki?

I found the hints in MacBuntu-OS theme.

-Thanks