The theme has many design options available in the Customizer -> Styling options that help you control design of your website. Some of those options are available for pages/posts individually inside the “Design Options” box available for each page/post edit screen. Design options always overwrite the global settings when changed. Design options also contain a couple of different option than the global options such as “Customize Menus” and “Sidebars”.
For example, let’s say you have selected “Header Stye 1″ from the Customize > Styling Options > Header Options to be used as the global setting for your entire website. But a page you are working needs to be”Header Stye 2”, then you can adjust it for the page by using the “Design Options”.