How to resize images with css?

Question

css

There are divs with percentage height and width, how to fit the image so that it has a width and height not exceeding the values ​​from the divs?
Preferably in pure css. Thanks in advance!

Answer 1

background-size: contain;
or if the picture

img {
max-width:100%;
max-height:100%;
}

Answer 2

max - width, max - height