align-content:space-around is defined to add equal spacing between the flex items vertically relative to the flex container on the cross axis (ie: vertically). Notice how it doesn't affect alignment on a per line basis- that's why flex item #2 isn't centered relative to #3 and #4. To do this, we should use the property "align-items" and set it to "center" as well.
align-content:space-around
align-items
center