This visual uses a Deneb/Vega template made by Davide Bacci. My experience is with Vega-Lite, which uses a different and simpler syntax. So my first thought would be to post to where Davide Bacci (or another Vega user) could comment properly (Stack Overflow).
That being said, I took a quick look and did have some success when I changed the signal that updated the width property.