Then, right-click the blank on the Windows desktop to choose Personalization, go to Background > Picture to choose Browse so that you can add the downloaded wallpaper to Windows 10. To do this work, you can firstly search for Mac OS X default wallpapers in Google, click Images to continue and then right-click one to choose Save image as to store it in a folder. This way, the Windows system has a similar appearance to the Mac.
To make Windows 10 look like Mac, the first thing you should do is to choose a Mac OS theme for Windows 10. Read More Install a Mac OS Theme for Windows 10
