[Vuejs]-Cant display full screen image background

It’s because the container is not at 100% height,
html and body should be 100% height (even for your wrapper class "BG"), otherwise the height will be defined by its content.

I think this is because you are using some sort of router-view to display the route, but the body also contains a navbar (as seen in the picture). You would need to use some sort of layout or meta data associated to the route to let the main layout page change the background-image accordingly.

Kinda like used here so that you can define the background-image from the layout.