The Gnome System Settings dialog doesn’t offer much malleability. If you’re serious about customising Gnome, you’ll need to use the Gnome Tweaks app. Although it isn’t an official Gnome app, many Gnome-based distros bundle it by default so you might already have it installed. If not, grab it using your distro’s package manager, since it’s in the official repositories of virtually all desktop distributions.
Using the tool is fairly simple. The different tweaks are listed under self-explanatory categories such as Appearance, Desktop, Top Bar and Workspaces. You can tweak the appearance settings of the desktop, display icons on the desktop, tweak the top panel, change the behaviour of the Windows and Workspaces, and a lot more.
From under the Appearance section you can switch to any shell or application theme you’ve downloaded from gnome-look.org. The Desktop section enables you to show icons and place some common ones such as the Home folder, Trash folder, Mounted Shares and Network Servers on the desktop. After you’ve activated this tweak, you’ll also be able to create documents and folders on the desktop. You can also manage the installed extensions using the Gnome Tweaks. Remember to visit the Windows section to bring back the minimise and maximise buttons in the windows.
You’ll have to first install the User Themes extension before you can change the appearance of the shell with a shell theme.