flex-direction

The flex-direction CSS property sets how flex items are placed in the flex container defining the main axis and the direction (normal or reversed).

Note that the values row and row-reverse are affected by the directionality of the flex container. If its dir attribute is ltr, row represents the horizontal axis oriented from the left to the right, and row-reverse from the right to the left; if the dir attribute is rtl, row represents the axis oriented from the right to the left, and row-reverse from the left to the right.

/* 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;

/* Global values */
flex-direction: inherit;
flex-direction: initial;
flex-direction: unset;

The following values are accepted:

row

The flex container's main-axis is defined to be the same as the text direction. The main-start and main-end points are the same as the content direction.

row-reverse

Behaves the same as row but the main-start and main-end points are permuted.

column

The flex container's main-axis is the same as the block-axis. The main-start and main-end points are the same as the before and after points of the writing-mode.

column-reverse

Behaves the same as column but the main-start and main-end are permuted.

Using the flex-direction property with values of row-reverse or column-reverse will create a disconnect between the visual presentation of content and DOM order. This will adversely affect users experiencing low vision navigating with the aid of assistive technology such as a screen reader. If the visual (CSS) order is important, then screen reader users will not have access to the correct reading order.

• Flexbox & the keyboard navigation disconnect — Tink
• Source Order Matters | Adrian Roselli
• MDN Understanding WCAG, Guideline 1.3 explanations
• Understanding Success Criterion 1.3.2 | W3C Understanding WCAG 2.0

row | row-reverse | column | column-reverse

HTML

<h4>This is a Column-Reverse</h4>
<div id="content">
  <div class="box" style="background-color:red;">A</div>
  <div class="box" style="background-color:lightblue;">B</div>
  <div class="box" style="background-color:yellow;">C</div>
</div>
<h4>This is a Row-Reverse</h4>
<div id="content1">
  <div class="box1" style="background-color:red;">A</div>
  <div class="box1" style="background-color:lightblue;">B</div>
  <div class="box1" style="background-color:yellow;">C</div>
</div>

CSS

#content {
  width: 200px;
  height: 200px;
  border: 1px solid #c3c3c3;
  display: flex;
  flex-direction: column-reverse;
}

.box {
  width: 50px;
  height: 50px;
}

#content1 {
  width: 200px;
  height: 200px;
  border: 1px solid #c3c3c3;
  display: flex;
  flex-direction: row-reverse;
}

.box1 {
  width: 50px;
  height: 50px;
}

Result

• CSS Flexbox Guide: Basic Concepts of Flexbox
• CSS Flexbox Guide: Ordering flex items