There’s something wrong with this picture. Actually, there’s something right that normally wouldn’t be — can you see what it is? (Hint: follow the dotted lines.)
Notice how everything lines up perfectly? Normally there’s a three pixel horizontal shift between List and Form views, but there isn’t in this case. Can you see why?
This is a very old trick, and I don’t know who first came up with it, but Danny Mack showed it to me many years ago: add a vertical line to the very left of the Detail layout (to simulate the one that FileMaker provides automatically for list views) and shift everything rightward by three pixels. That way your screen won’t “jump” as the user navigates between form-view and list-view layouts.