CSS:使一个块元素填充父元素的整个空间？

.child-element {
  width: 100%;
  height: 100%;
}

.parent-element {
  display: flex;
  justify-content: center;
  align-items: center;
}

.child-element {
  flex-grow: 1;
}

.parent-element {
  display: grid;
}

.child-element {
  grid-column: 1 / -1;
  grid-row: 1 / -1;
}