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/config/index.ts

@@ -1,9 +1,11 @@
 import { DocsConfig } from "types"
 import { sidebarConfig } from "./sidebar"
 
+const baseUrl = process.env.NEXT_PUBLIC_BASE_URL || "http://localhost:3000"
+
 export const config: DocsConfig = {
   titleSuffix: "Medusa v2 Docs",
-  baseUrl: process.env.NEXT_PUBLIC_BASE_URL || "http://localhost:3000",
+  baseUrl,
   basePath: process.env.NEXT_PUBLIC_BASE_PATH,
-  sidebar: sidebarConfig,
+  sidebar: sidebarConfig(baseUrl),
 }