docs: simplify navigation and layout

docs/book.toml

@@ -13,6 +13,6 @@ create-missing = false
 [output.html]
 default-theme = "navy"
 preferred-dark-theme = "navy"
-additional-css = ["theme/lore.css"]
+additional-css = ["theme/layout.css"]
 fold = { enable = false }
 search = { enable = false }