Custom Element Enhancements

[shshaw]

Great approach to tweaking CSS vars! I've built bespoke little controls for this so many times but having a drop-in would be super helpful.

For Custom Elements:

1. Allow attributes to control simple config<slide-vars open scope="#elem">
2. Allow multiple instances. You could have 4 or 5 demos on a page with the controls right next to them, provided Slide Vars can use non-fixed positioning and you can easily change the scope via attribute
3. A scope="parent" value that indicates these are controls for this container

<div class="box-example red">
  <slide-vars scope="parent" />
</div>
<div class="box-example blue">
  <slide-vars scope="parent" />
</div>