Automatically make text lines foldable salient

Text folding is pretty powerful ! But capabilities to automatically highlight text lines that have folding arrows can be a further benefit as illustrated following:

I feel it not a hard task, can some guru achieve this, maybe through a plugin ?

Should be easy with a CSS snippet. View > Toggle Developer Tools, then select the arrow tool in the very upper left and hover over a foldable line. The most prominent text in the box that pops up will be that item’s class; if it nothing in it sounds related to folding, check the HTML markup highlighted in the upper section of the developer pane to see what’s between the quotes after class=. Try it both folded and unfolded, as eachh state may have a separate class.