[css-forms-1] Define base appearance for datalist elements

[lukewarlow]

It is mentioned in the draft but it would be good to get that fleshed out more (as it's largely the same as selects pickers behaviour).

[mfreed7]

+1. In particular, datalist is mentioned, but many more details are needed. E.g. is there a ::picker(datalist) or something? And which controls support it? Etc.

[mfreed7]

One more comment here - datalist already interacts with the in-page control in some browsers in some cases. That feels like that should be standardized also. For example:

<input type=range list=foo>
<datalist id=foo>
  <option value=1>
  <option value=65>
  <option value=90>
</datalist>

Renders like this in Chrome: