graph LR
subgraph outer
    A
    subgraph inner
        B
    end
    C
end
D
---
+-----------+
|   outer   |
|           |
|           |
|   +---+   |
|   |   |   |
|   | A |   |
|   |   |   |
|   +---+   |
|           |
| +-------+ |
| | inner | |
| |       | |
| |       | |
| | +---+ | |
| | |   | | |
| | | B | | |
| | |   | | |
| | +---+ | |
| |       | |
| +-------+ |
|           |
|           |
|           |
|   +---+   |
|   |   |   |
|   | C |   |
|   |   |   |
|   +---+   |
|           |
+-----------+
             
             
             
    +---+    
    |   |    
    | D |    
    |   |    
    +---+    
