How to make a proper Holy Grail Layout with scrolling on Flexbox?

Question

css

There are different layout options "navigation + content + footer" on flex, for example - https://gridlayout.io/demos/holy-grail.html a lot and vertical scrolling should appear in it. Instead, the whole layout just goes down in height, and scrolling does not appear.
What needs to be changed so that it does not change its height, but goes into scrolling if necessary?

Answer 1

main {
   flex: 2;
   overflow: auto;
}

Answer 2

Fix height and allow scrolling:

main {
    height: 100vh;
    overflow-y: auto;
}