Flex-box: Align last row to grid

Question

I have a simple flex-box layout with a container like:

.grid {
  display: flex;
  flex-flow: row wrap;
  justify-content: space-between;
}

Answer 1

If you know the width of spaces between elements in the row and the amount of elements in a row, this would work:

Example: 3 elements in a row, 10px gap between elements

div:last-child:nth-child(3n+2) {
  flex-grow: 1
  margin-left: 10px
}