Can't see position in a scrolled window without scrolling or moving the mouse

[Iain Lane]

With 3.16's new scrollbars I can't tell how far I am through a document unless I either scroll it or move my mouse cursor on the window, both of which cause the scrollbar to be revealed.

We discussed this a bit and allowing this to be themed would require making the fade out a CSS animation so that we could transition to a different state than full transparency. Currently the code calls gtk_widget_set_opacity() itself to step down to transparent.