SCROLLBARS & $(window).scrollTop()
What I have discovered is that calling such functionality as in the solution thankfully provided above, (there are many more examples of this throughout this forum - which all work well) is only successful when scrollbars are actually visible and operating.
If (as I have maybe foolishly tried), you wish to implement such functionality, and you also wish to, shall we say, implement a minimalist "clean screen" free of scrollbars, such as at this discussion, then $(window).scrollTop()
will not work.
It may be a programming fundamental, but thought I'd offer the heads up to any fellow newbies, as I spent a long time figuring this out.
If anyone could offer some advice as to how to overcome this or a little more insight, feel free to reply, as I had to resort to show/hide onmouseover/mouseleave instead here
Live long and program, CollyG.