And boy shorts for her

 The white pairs were made first, mainly as prototypes for a swim short pattern I am developing. They are made from a two-piece pattern with centre seams front and back. For the blue pair, I added a panel in the crotch (am I right in thinking it's not really a gusset?) to avoid a centre seam running through the crotch.

The blue pair were eked out of scraps left over from my husband's boxer shorts. I wouldn't normally have chosen such a wide elastic, but I wanted these pants to match the boxer shorts. So much fun to have matching undies!

I attached the elastic with a wide zig-zag with the idea of adjusting it after I wear them a bit to check how tight I prefer it. I may also upgrade to the better elastic if I see it holds up well in my husband's boxer shorts (I expect so) and I restock.