XF 2.3 Sticky elements in sideNav ?

[makanyane]

I've got the last element of my side bar sticking nicely to the top of view in long threads by using:

.p-body-sidebar > div:last-child { position: sticky; top: 68px; }

I'm failing miserably to get anything similar to work for the sideNav on the left, the div blocks for that are in
.p-body-sideNavContent but

 .p-body-sideNavContent> div:last-child { position: sticky; top: 68px; background:red; }

gets me a red background on the item I want to stick, but it doesn't stick...

I've tried various different position options on the elements that contain .p-body-sideNavContent but haven't found anything that works yet

I assume my problem is that the whole .p-body-sideNavContent and its OCM container are scrolling out of view? Sticking the whole of sideNav or sideNavInner doesn't give me what I want, as I need the Nav bar to start scrolling with the page, but just stop near the end of it's content...

any ideas?