feat: Updates styles for sidebar and articles list view.

Sources/Docs/Templates/BaseLayout.swift

@@ -58,7 +58,10 @@ private func siteHeader(_ section: Section) -> Node {
           }
         }
       }
+      // TODO: Explore search being hidden / triggered by a button and hover above
+      //       the page content.
       div(class: "font-avenir w-full pt-4 px-8", id: "search") {}
+      div(class: "mt-2 mb-0 w-full border-b border-slate-200")
     }
   }
 }