docs: fix download button + other fixes (#8032)

- Fix text of download button
- Small fix to styling on small devies
- Fix mobile sidebar items using incorrect base url

www/apps/book/components/Navbar/index.tsx

@@ -13,7 +13,7 @@ const Navbar = () => {
     () =>
       getNavbarItems({
         basePath: config.baseUrl,
-        activePath: basePathUrl(""),
+        activePath: basePathUrl(),
         version: "v2",
       }),
     []