I used a Tabs control which is simply like a button that doesn't depend on any child,
to align it to the top I put it inside a VboxContainer.
To add new tabs (Contrary to the intuition of adding or duplicating the Tabs control) I using code:
And to show the close button on the selected tab:
I still have to see how to display a custom tab with the + symbol and not show the close button when clicked...