Flex children are just that: display: block or display: inline don't have any affect once display: flex is defined on the parent.

Flexbox is controlled inside --> out: The size of the children affect the size of the parent. Grid is outside --> in: the size of the parent is specified and the children fit inside.

Defaults: flexbox by default uses the 'best' size for the children. It doesn't expand them, but it will shrink them if necessary.
flex-shrink: 1;
flex-grow: 0;

If you have multiple rows and columns, and you want them consistent, grid is the better choice

width is the same as flex-basis IF you are using columns