[csswg-drafts] [css-backgrounds][css-logical-props] Define logical values for <side-or-corner>

jonathanKingston has just created a new issue for 
https://github.com/w3c/csswg-drafts:

== [css-backgrounds][css-logical-props] Define logical values for 
<side-or-corner> ==
In [the linear gradient 
syntax](https://drafts.csswg.org/css-images-3/#linear-gradient-syntax)
 there currently isn't the ability to use logical gradient sides.

Can we consider adding the ability to use:

```
background: linear-gradient(to block-end, white, black);
```

Related to: #549 

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/974 using your GitHub 
account