Ok so I apologize if the title of the question is confusing but see this:

So there is a blue container in the bottom left and 2 in top right corner of the main grey container. How do implement something like this in flutter. I am guessing there are two columns here one for left side panel and one for main grey container in right. How to make those blue containers as shown in the image that is part of both the columns?

I found there is a widget named OverflowBox, Maybe I can put this widget as a child in the main grey container but how would it overlap the left column and also how do I make it appear as a separate widget with those rounded corners between them