Share a site
Within a collection, it is possible to share a site's items with all the other sites of the environment. A shared site acts as a "master" site. This means that the content items that you create and configure there (such as components, partial designs, and page designs) can be consumed by other sites from the same environment.
For example, a marketer creates partial designs relevant for all sites, and instead of having to maintain them as individual instances, they save their work in a shared site, making the partial designs available to all content authors.

To share one site's items with all other sites in the collection:
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In Channels, in the collection of your choice, on the tile of the site you want to share, click the Options menu
> Settings. -
On the General tab, go to the Site sharing section and click the switch Share site.
From then on, when working with any other site from that collection in the Pages editor, you will be able to access all the items from the master site, in addition to the items specific to the site you are working on.
You can later choose to unshare a site by unchecking the Site sharing option. In this case, the data sources, presentation, and settings will no longer be available for use from the other sites of the collection. However, everything that was used while the site was shared will remain as it is on the existing pages, and the links created previously will not be broken.