This was intentional to highlight the borders more obviously.

The test app has a key to turn that off see https://github.com/joshka/ratatui/blob/joshka/cell-borders/C...

The side gaps were for for making it feel balanced in the screenshots and visualizations to be able to show where the borders line up with cells easily etc. It wouldn't be what I'd use in a real app.

One thing to note though is that some things which are "wrong" can be aesthetically pleasing to look at and may be the actual best UX in certain situations. There's a lot of new design principle work (especially in macOS / iOS) that is about things going past the edge, or being overlaid with floating things. Some of this is "wrong" some of it is wrong, and some of it sitting in in the useless gap beteen the two. ;)