Background Images

So I am frustrated, for the last 3 hours I have been trying to set up a background image for my website copying the way the you tube tutorial was done from the Tesla site. I have not been able to do this because I do not know the measurements of the pictures he used on the tutorial. I wonder if someone can tell me what I am doing wrong. I found a button that made the image responsive but I cannot seem to find where it was. When I change the size of the devices the image get lost.

Than you in advance for the help.

1) take a look at the actual Tesla site for image specs as I’m sure the devs took the files from there 2) alternatively (and likely raiser) follow the resources link that has all the images used in the tutorial in the YouTube video description.

Thank you for the response... did not thinkt about that!!!!