2 components share the fullscreen: list and image in a container

I have created a container (fullscreen) and added a list and image.
The container does fit the fullscreen (at least that’s what I assume)
How do I tell the two guys inside that they should resize themselves to share all the space the container offers?
Am I even supposed to use a container for this?

You can define in advanced (just after custom) the % of each component is 50 high.
(If I understood what you are asking for)