images/thumbnails:
box-shadow: 0 0 4px rgba(0, 0, 0, 0.5);
aren't consistent with the 

Contextual Modals: 
box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
This should probably be a note to resolve with the Y! Design Language folks. Maybe inconsistent is what they will want. Maybe images should use drop shadows as "soft borders" and Contextual Modals should have offset looking drop shadows.