WIP: add support for nested folders and collection

src/popup/scss/base.scss

@@ -374,6 +374,7 @@ content {
     align-items: center;
     height: 100%;
     flex-direction: column;
+    flex-grow: 1;
 }
 
 .no-items {

src/popup/scss/box.scss

@@ -475,3 +475,8 @@
         }
     }
 }
+
+.stacked-boxes {
+    display: flex;
+    flex-direction: column;
+}