Change the below attribute in the body tag in the Views/Shared/_layout.cshtml file to set the detached layout style.

How to add new menu items/change menu items?

To add, change or remove menu items from the left side navigation, simply edit in file Views/Shared/_Sidebar.cshtml. The change would reflect in all the HTML files automatically.take care of including the Views/Shared/_Sidebar.cshtml file content in all HTML pages.