Styling tweaks for CompactPostDisplay
Styling tweaks for CompactPostDisplay

This just fixes the display of the thumbnail a little bit and adjusts
the 'link' icon a little bit as well (to match up better with the
mocks).

closes #1305
pr #1308

mitodl/open-discussions,mitodl/open-discussions,mitodl/open-discussions,mitodl/open-discussions,mitodl/open-discussions