no, was refrencing to my css/html above ...
the very, very simplest solution is aspect-ratio - CSS: Cascading Style Sheets | MDN ... but it's quite new and excludes some browers: CSS property: aspect-ratio | Can I use... Support tables for HTML5, CSS3, etc
again, the scripted version should be easy too: it's copy 'n paste:
https://forums.tumult.com/t/creating-a-flexible-tumult-hype-document-within-a-div-with-no-set-height/13224/20
in the end as always, please post a sample file and it'll be easier for anyone to help 