mode: center for changelog & add docs for center mode (#444)

* mode: center for changelog

* add center mode

Author: hahnbeelee

changelog/overview.mdx

@@ -1,7 +1,7 @@
 ---
 title: "Product Updates"
 description: "New updates and improvements"
-mode: "wide"
+mode: "center"
 ---
 <Update label="December 2024">
   ## Authentication

page.mdx

@@ -146,6 +146,18 @@ mode: "custom"
 ---
 ```
 
+### Center Mode
+
+*Center Mode* removes the sidebar and the table of contents, and centers the page content. This mode is great for changelogs
+or any page where you want to focus on the content.
+
+
+```md
+---
+mode: "center"
+---
+```
+
 ## External Links
 
 If you want the sidebar to open an external URL, you can set the `url` metadata