Don't use any padding in thumbnails

app/assets/stylesheets/preview.sass

@@ -23,7 +23,6 @@
   .thumbnail
     padding: 0
     background-color: #000
-    padding: 8px
     border: 0
     border-radius: 3px
     border-bottom-left-radius: 0
@@ -36,6 +35,7 @@
     border-bottom-right-radius: 3px
     border: 1px solid #eee
     border-bottom: 1px solid #ddd
+    border-top-width: 0
 
     .author-avatar
       float: left