I want to make some UI changes in QGC

I want to make some UI Changes in the highlighted parts in QGC. I am having trouble finding the files that contain the code for changing the UI. Can someone tell me where i can find the files? I have attached the screenshot of that below

There are some youtube clips showing how to modify certain things within QGC.

However, why bother? …there is this very little known feature whereby whilst video streaming you can double click (or fast double tap on touch-screens) any area other than those showing instruments/icons and you’ll get a full screen view.
→ Repeat to go back to normal view.

Duplicate topic here :