How to make background image fit in all resolutions.

Question

https://code.sololearn.com/W458cqcjgstX/#html
(sorry for english)
i this code i gave background img certain height but the problem is if i open on my pc it will not show complete img while on phone it does how can i make it to fit all resolution wheater you use mobile or pc .(iam not good at designing so there might be other common mistakes) .

Answer 1

Use background-size:100% 100%;
As cover means aspect ratio

Answer 2

Use this:
<meta name="viewport" content="width=device-width, initial-scale=1.0">

Answer 3

thanks