Main size and cross size

There's something called the main size and cross size, as shown here:

By default, the main size is the width and cross size is the height, but this can change if you modify the flex-direction, something we'll learn about in the next section.

Get Mastering CSS now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.