Here's an example in `crates/gpui/examples/corner_radii.rs`

![CleanShot 2023-08-12 at 11 06
09@2x](https://github.com/zed-industries/zed/assets/1789/1b5992ac-f7ef-45d8-b8c2-f0e677b07dd9)

@iamnbutler, in the themes, anywhere we have a container style can now
take either a `corner_radius` or a `corner_radii` field, both of these
fields can either have 1 number (for all 4 corners) or a an object like:

```
{
  top_left?: number,
  top_right?: number,
  bottom_left?: number, 
  bottom_right?:number 
} 
```

Fields that are not included in this second representation default to 0
corner radius.