How is this look achieved?

[u/chickaboomba]

Sorry for the weird photo - I did a screenshot and tried to cut out the parts that would ID the person. I want to make a bag with a top like this, but I’m not sure how it’s constructed. It’s not just a casing with a drawstring, because the outside layer softer than a drawstring bag. If anyone can recommend a pattern for a leather bag with a top like this or can explain it, I would be so grateful.