Merge branch 'sub-navigation-styles' into 'develop'

Another PlaceholderStatus style fix

Closes #787

See merge request soapbox-pub/soapbox-fe!945

app/styles/components/columns.scss

@@ -956,7 +956,7 @@
   // ScrollableList
   .slist .item-list > article:first-child,
   // ScrollableList placeholders
-  .slist .item-list .slist__placeholder > .material-status:first-child,
+  .slist .item-list .slist__placeholder:first-child > .material-status:first-child,
   .slist.slist--flex .item-list > .material-status:first-child,
   // Thread
   .material-status:not(.material-status + .material-status) {