CSS writing-mode

The CSS writing-mode property specifies whether lines of text are laid out horizontally or vertically and the direction in which blocks progress.

Note that the content of replaced elements do not rotate due to the writing mode: images and external content such as from iframes, for example, remain upright, and the default object size of 300pxÃ—150px does not re-orient.

Syntax

Which means that it can be any of those three values.

In other words, it can be any of the following:

Possible Values

Below is an explanation of the values.

horizontal-tb: Top-to-bottom block flow direction. Both the writing mode and the typographic mode are horizontal.
vertical-rl: Right-to-left block flow direction. Both the writing mode and the typographic mode are vertical.
vertical-lr: Left-to-right block flow direction. Both the writing mode and the typographic mode are vertical.

In addition, all CSS properties also accept the following CSS-wide keyword values as the sole component of their property value:

initial: Represents the value specified as the property's initial value.
inherit: Represents the computed value of the property on the element's parent.
unset: This value acts as either inherit or initial, depending on whether the property is inherited or not. In other words, it sets all properties to their parent value if they are inheritable or to their initial value if not inheritable.

Basic Property Information

Initial Value: horizontal-tb
Applies To: All elements except table row groups, table column groups, table rows, table columns, ruby base container, ruby annotation container
Inherited?: Yes
Animatable: Not animatable

CSS Specifications

The writing-mode property is defined in CSS Writing Modes Level 3 (W3C Recommendation, 10 December 2019)

Vendor Prefixes

For maximum browser compatibility many web developers add browser-specific properties by using extensions such as -webkit- for Safari, Google Chrome, and Opera (newer versions), -ms- for Internet Explorer, -moz- for Firefox, -o- for older versions of Opera etc. As with any CSS property, if a browser doesn't support a proprietary extension, it will simply ignore it.

This practice is not recommended by the W3C, however in many cases, the only way you can test a property is to include the CSS extension that is compatible with your browser.

The major browser manufacturers generally strive to adhere to the W3C specifications, and when they support a non-prefixed property, they typically remove the prefixed version. Also, W3C advises vendors to remove their prefixes for properties that reach Candidate Recommendation status.

Many developers use Autoprefixer, which is a postprocessor for CSS. Autoprefixer automatically adds vendor prefixes to your CSS so that you don't need to. It also removes old, unnecessary prefixes from your CSS.

You can also use Autoprefixer with preprocessors such as Less and Sass.