Could use some help making a lid for my project box

StillMaker

I'm working on a 3D printable case for a circuit board & switch. I've got the bottom part of the case figured out, now I'm trying to make a lid for it. I'm thinking a flat piece that matches the size of the box, then extrude down into the box 1-2mm for a press-tight fit. I'm open to other ideas. I want something simple. I don't anticipate having to open the box very often after initial setup, so the lid does not need to be complicated, a simple press fit will be fine I think.

I've been working on it but not getting anywhere. The inside & outside of the box has complicated curves (sketch fillets) and I'm having trouble drawing a box such that it will end up with a matching fit. Can someone help me out a little? I'd appreciate it, thanks.

Here is my document:
https://cad.onshape.com/documents/206e9c2ea893eb969d1461f5/w/8dd1943f9b8d66de9d5347f4/e/6696d492fd9c4651265bf8b8?renderMode=0&uiState=661f4125a7f31b2dc9af77ba

eldon_brown

Here is one approach:

https://cad.onshape.com/documents/52b3235e30d6e3b23afef855/w/1fa60cfb0e8539e4756dc1c7/e/ca2667099e2c706e334e435e?renderMode=0&uiState=661f4f55e637801c9bfc3d2b