After doing all these, I still cannnot scroll down to the bottom of the “Terminology” page. But everything is ok when I deal with pictures. Is there any difference between pictures and text?
This doesn’t work. The StackPanel provides an infinite vertical height to its children, thus the ScrollViewer sizes to completely contain its children. This means the outer StackPanel simply exceeds the size of the screen. This is why you can’t scroll, because the ScrollViewer has a large enough size to display everything.
In this case you can simply remove the outer StackPanel, since it has only one child.
If you wish to have a vertical layout that fills the screen you can use either a Grid or a DockPanel.