For syntax highlighting I use Highlight.js with a custom theme.

Automatic language detection has been turned off, so you will probably want to specify the programming language you use like this

```rust
fn main() {
    // Some code
}
```

Like the rest of the theme, the files used for syntax highlighting can be overridden with your own.

• highlight.js normally you shouldn't have to overwrite this file, unless you want to use a more recent version.
• highlight.css theme used by highlight.js for syntax highlighting.

If you want to use another theme for highlight.js download it from their website, or make it yourself, rename it to highlight.css and put it in src/theme (or the equivalent if you changed your source folder)

Now your theme will be used instead of the default theme.

There is a feature in mdBook that lets you hide code lines by prepending them with a #.

# fn main() {
    let x = 5;
    let y = 6;

    println!("{}", x + y);
# }

Will render as

# fn main() {
    let x = 5;
    let y = 7;

    println!("{}", x + y);
# }

At the moment, this only works for code examples that are annotated with rust. Because it would collide with semantics of some programming languages. In the future, we want to make this configurable through the book.toml so that everyone can benefit from it.

If you think the default theme doesn't look quite right for a specific language, or could be improved. Feel free to submit a new issue explaining what you have in mind and I will take a look at it.

You could also create a pull-request with the proposed improvements.

Overall the theme should be light and sober, without to many flashy colors.