There is only one Islamic theme for Sabily 9.10 version but I already suggested Sabily team to add many Islamic themes in the next Sabily Manarat version. Anyway, if you want to get any other themes there are many on the gnome homepage. Lets see what they have there.
On System/Preferences, click on Appearance.
Appearance Preferences windows appeared. Click on Get more themes online. Make sure you're online.
You will be direct to Gnome Art homepage.
Controls themes page.
Window Borders themes page.
Icons themes page.
Splash Screens themes page.
Login Screen themes page.
You also can get many background picture here at Backgrounds page.
There are hundreds or thousands themes that you can get here. You also can upload your owned themes that you like to share with other Linux user here. Happy download new themes.