What problem does this solve or what need does it fill?

The CSS layout specifications allow for reversed layout dependent on the direction property. This allows UI layouts to reflect the layout conventions of users of RTL languages (which conventionally start from the right) in addition to users of LTR langauges that usually expect layouts which start from the left.

What solution would you like?

Note: A PR for this has been started: #736

• Add a direction style with Ltr and Rtl variants
• Add support for generating this style in the test generator
• Update Flexbox algorithm to use this style
• Update CSS Grid algorithm to use this style
• Update Block algorithm to use this style

Additional context

More context on MDN