This is the same engine the Safari browser uses so can be used to check and debug css without a mac.
Although both Safari and Gnome Web both use webkit they are not the same browser and may have differences.
Gnome Web has familiar looking web tools which can be brought up with
The elements tab¶
The elements tab shows the HTML and allows you to hide and edit elements.
You can open the Extra Details Sidebar to view CSS and other details linked to and element by pressing
CTRL + Alt + 0.