tweak to small avatars

wagtail/wagtailadmin/static/wagtailadmin/scss/components/formatters.scss

@@ -50,7 +50,7 @@
 
     &.avatar-on-dark:before{
         color:$color-grey-2;
-        border: 2px solid $color-grey-2; 
+        border-color:$color-grey-2; 
     }
 }
 

wagtail/wagtailadmin/static/wagtailadmin/scss/components/main-nav.scss

@@ -291,6 +291,10 @@ body.explorer-open {
                 margin:0 0.7em 0 0;
                 border:0;
                 float:left;
+
+                &:before{
+                    text-shadow:none;
+                }
             }
             em{
                 width:120px;