Answers for "place content center"

align div content center

.child {
  ...
  margin: 0 auto;
}

place-content css property

This property is a shorthand for the following CSS properties:
1-align-content
2-justify-content

Possible values => start|flex-start|end|flex-end|right|left|center|
space-around|space-between|space-evenly|baseline|stretch