Try placing your ViewBox
at the root level instead.. it should look something like this:
<ViewBox>
<Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
...
</Grid>
</ViewBox>
You may want to play around with the Stretch
property of the ViewBox
to achieve your desired result. But I'd reckon to use the "Fill"
option.
I've been using this method for my games and apps to adapt to different screen ratios and sizes.