Two containers side by side inside a row - how to set the height of the container on the left equal to that of the container on the right?

I am stuck so any help would be really appreciated :D

Here is my setup:

1) Inside a row, I have 2 containers like that:

Here are the properties for the container on the left:

and here are the properties for the container on the right:

as you can see, the container on the right has no height, as its heights depends on the height of the elements with which it gets filled in with.

I am currently setting the height of the container on the left with a variable I am calculating, but I can not get it to work properly when the amount of data stored on the container on the right changes.

I want the two containers to have the exact same height (which is unknown until the data are fetched). Please take into account the container on the left only contains a colour, it has nothing in it. Any ideas how to force the container on the left to have the same height as the container on the right?