The Box model is not just a simple layout of lined up boxes in parallel, but can also be nested to create more complex layouts. You can check the parent-child relationship of the elements in the Layers panel on the left of the screen.
A parent box can contain many child boxes, and a child box can contain more grandchild boxes to create multiple nested structures.
To make nested structure
Select the box that will be the parent box to contain other boxes.
Drag the Box you want to add from the Add menu on the left or from the design you already have in place, and drop it into the parent box.
※ If the child box is larger than the parent box, you are not able to add it. Please make sure that the orange shadow indicating the landing point is displayed in the parent box before dropping it.