How to make such an adaptive image on the site?

Question

css

https://qiwi.com/
if you reduce the screen size (Ctrl + -) then the picture will adapt to the screen width.
How can I do this on my site?

welovepavel.esy.es/Kivi/HTML.html
zy.please give the code if you can.
ZY2. Don't talk about F12, I've already looked ...
Thank you!

Answer 1

https://jsfiddle.net/QW01_01/auypeqo3/

Answer 2

for the picture, just write the styles:
although it is a little more complicated there: it is really like in the first example made by the background of the block with the style
background-size: cover;