Hi Nicolas,
You can use a container, like the Canvas.

But you have to put it down before you put the elements in it.
If you have exsiting elements, you'll have to edit the source. So if you have 3 elements that already exist, and you want to move them into the canvas below:

You have to edit the code to look like this:

You'll also have to adjust the position of all the elements (left, top, etc). Those will now be relative to the canvas and not the top of the panel.
You should also look at the simple grid container. It's also very useful.
If you watch this video, you'll learn a lot about containers.
https://www.rossvideo.com/gallery/creating-a-mockup-of-your-panel/
#DashBoard