WHAT I WANTED DO:
I’m going to stop writing this part. What I want to do is the same for each: apply something I learned to a geometric, totally bogus design born of my wacko imagination.
Until I want to do something more novel, I’m going to leave this out.
WHAT I LEARNED:
How to clip a line and fill it with its own color.
How to apply a gradient/fade to an object.
WHAT I DID:
The scissor tool is pretty damn awesome. But I don’t think that’s the technically-right way to do what I want. But it works for the time being.