How to make a scrollable container with dynamic height using Flexbox

One of the hidden features of Flexbox is the ability to make a flex child scrollable. In the past, if you wanted to make a scrollable container, you had to give the container a predefined height. In other words, the height could not be based on the size of its surrounding content. You had to use pixels, percentages, or absolute positioning if you wanted an element’s content to scroll. With Flexbox

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"flex-grow: 1" heightが不明の要素に対する残りの要素をスクロールさせたいとき