【flex-direction】　

　　The flex-direction CSS property specifies how flex items are placed in the flex container defining the main axis and the direction

/* The direction text is laid out in a line */

flex-direction: row;

/* Like <row>, but reversed */

flex-direction: row-reverse;

/* The direction in which lines of text are stacked */

flex-direction: column;

/* Like <column>, but reversed */

flex-direction: column-reverse;

　　

参考：https://developer.mozilla.org/en-US/docs/Web/CSS/flex-direction