Is there a CSS rule that would match elements based on their width? If not, would it be interesting to propose that in the standard?
One could do something like
That might become inconsistent because new elements could be unexpectedly affected. I would just add a class that defines {wrap: nowrap;} to any elements in your html. Or if the element width changes on resize, just use some js.
window.onscroll = function(){
var elementWidth = document.getElementById('elementID').style.width;
if(elementWidth < 200){ .. do something .. }
else{ .. reverse changes .. }
}