I’ve dug into this extensively and written a few forum posts including this one - And it’s a terrible solution: Collapsable Width
@edward.w.douglas is technically correct - That method DOES collapse width, but it’s only based on parent width - It accepts no other logic to it. You can’t dynamically say - “If I don’t need this button, hide and collapse the width” - Which is what I think you’re wanting.
My best advice after struggling with this is to design around it. If you go the Javascript route and try to hack around it, you’ll run into other gremlins… which is why I dislike my own solution… It broke the responsive engine.
Just my 2 cents.