The default behavior of Grid Auto Flow is to layout the elements by row, working along the row until there are no more slots then moving on to the next row. If a row is not declared then an implicit grid track will be created to hold the items.
You can change this behavior by using the
grid-auto-flow property. The default value is
row but you can also specify
column. The elements will then be laid out column by column, adding new columns if needed.