Is the header image cropped when the screen resolution is changed?

Question

Images

Site mowiless.ru
There is a picture in the header of the site. When I change the permissions of the site, the picture on the right is cut off. How can I make sure that the pictures are not cropped, but change along with the screen resolution?

Answer 1

.site-header {
    background-size: 100% auto;
}

Answer 2

And now how to make this image in the header the entire width of the browser, like the bottom image?
mowiless.ru