[css-forms-1] Fix double borders

[lukewarlow]

Fixes #11841

[lukewarlow]

cc @nt1m does this seem reasonable to merge? Or should I try and get a discussion in the group for which approach is best? Seems like a bug fix personally?

[nt1m]

It kind of depends on which way to go, if you want the more traditional slider style with the track smaller than the thumb, then maybe it makes more sense to remove the border from the host element rather the track.

Either way we go I'm fine accepting it as a bug fix in the short term, but it would be good to discuss that bigger decision in the WG.

[lukewarlow]

I've swapped to the other approach where the track has the border NOT the container. As you say for stuff like range where you might want the track to be smaller (even some switches are like this), it doesn't make sense for the border to be on the parent container.

[lukewarlow]

Going to merge as a bug fix but like you say we should have a wider discussion on this.