align the flex items vertically.

align-items: stretch;

flex item 1
flex item 2
flex item 3

align the flex items vertically.

align-items: flex-start;

flex item 1
flex item 2
flex item 3

align the flex items vertically.

align-items: center;

flex item 1
flex item 2

align the flex items vertically.

align-items: baseline;

flex item 1
flex item 2
flex item 1