sidebar: 2px margin between rows

This avoids rows blending together when hovering a row next to the
active one.

data/resources/style.css

@@ -265,6 +265,7 @@ login {
   animation-timing-function: ease-in-out;
   outline: 0 solid transparent;
   outline-offset: 2px;
+  margin-top: 2px;
 }
 
 .sidebar-list sidebar-row > * > box {