List The CSS Themes In Rust's syntect Syntax Highlighting Crate

```cargo
[dependencies]
syntect = "5.2.0"
```

use syntect::highlighting::ThemeSet;

fn main() {
  list_themes();
}

fn list_themes() {
  let ts = ThemeSet::load_defaults();
  ts.themes.iter().for_each(|theme| {
    println!("{}", theme.0);
  })
}