Strawman for article about adapting CSS style sheets to support bidi

Here's a rough outline of things to include in a proposed article, per 
our telecon discussion yesterday.

Anything i missed?  Any other comments?


title: Making your CSS style sheets support bidi text

- [ ] Use logical values
     - [ ] list values that currently work and those that don't
     - [ ] consider avoiding margin: a b c d; format, at least until 
browers support logical values (currently stuck in CSS), where it's easy
     - [ ] note that margin-inline & margin-block etc are a (useful) thing


- [ ] Convert the remainder is a possibility, though not the best approach
     - [ ] Use CSS Janus etc for converting non-logical values & properties
- [ ] Store this as a separate style sheet
     - [ ] not ideal approach, because small maintenance tweaks need to 
be made in 2 files, and all files need to call 2 style sheets


- [ ] Use a switch in your main CSS file (works much better)
     - [ ] ideally you'd use :dir(), but it only works in Gecko browsers 
at the moment (we'll be raising bugs & gap reports)
     - [ ] as a workaround, use :root[dir=rtl]