ScrollViewer doesn't scroll if cursor is not over a child element

[tomlm]

Repo

go to Image gallery

• Put mouse over the images and use mouse wheel => it scrolls
• Put mouse over background of scroll window and use mouse wheel => it doesn't scroll

Expected

Mouse wheel should scroll inside the entire rectangle of the scroll area.

[jinek]

I have been fixing several related issues. Had to set some background, even tho ttansparent, but not null, as I remember. It helped with datagrid and listbox scrolling.