Function to_html 

pub fn to_html<S: AsRef<str>>(
    str: S,
    theme: impl ColorTable,
    width: Option<usize>,
    font: Option<String>,
    mode: Option<Mode>,
    light_bg: Option<String>,
    dark_bg: Option<String>,
    font_size: Option<usize>,
    sourcemap: bool,
) -> String