I am new to godot , how can I add a highlight/pop-up/selection effect on the texturerect node which is inside a hboxcontainer/Scroll Container/window/control node . Like we scroll background apps in our smartphone, one is always at the top/highlighted.
Here’s the file
Please help 
What sort of effect do you want? You could apply a tint to one of them with self_modulate, you could put each element inside a margin control and tint the margin control of the selected thing to give it highlighted borders.
Godot’s control nodes can be themed, so if you use control nodes you can set things like what they look like when focused or pressed.
Can I scroll horizontally only 800 px at a time when swipe with the fingers left and right because the texturerect size is 800 px horizontally, and the current texturerect should be grow bigger (scale) kind of zoom out effect. Is it possible?
You should be able to set scale on the TextureRect, and there are various knobs you can tweak to control how it scales; see the documentation for TextureRect and its parents…