You should be able to use Anchors to allow your Control nodes to resize themselves to your viewport.
Take your top node Control and make sure its size fills the viewport; Edit > Expand to Parent (the root viewport is your top node’s parent in this case). Find the Anchor button and set it to Full Rect.
Anchors are applied relative to their parent. So with the TextureFrame as a parent of the top node Control, you can do the same: Expand to parent and Anchor Full Rect.