[doc] highlight the current page in the sidebar

docs/_themes/searxng/static/searxng.css

@@ -33,6 +33,9 @@ p.sidebar-title, .sidebar p {
   list-style-type: disclosure-closed;
 }
 
+.sphinxsidebar .current > a {
+  font-weight: bold;
+}
 
 /* admonitions
 */