How to make a full screen splash screen?

Question

css

Explain to the noob - how is the header image made up (and drawn) so that it completely covers one screen (laptop / tablet / mobile)?

It is not entirely clear how to make it so that the image does not crop on the bottom / sides, given that the screens are different (I understand for now that this is / height: 100% (?)

And what resolution should the image have in order for it to fit on different screens

Answer 1

height: 100vh;
vh is the visible height area,
vw is the widths
Can be said as 100%, or 20% only vh vw of the height width