Macro class 

class!() { /* proc-macro */ }

The class! macro for defining CSS classes with style properties.

Each class definition creates a CssClass function that can be used in html! via the class: attribute. Styles are automatically injected into the DOM on first use.

class! {
    pub container {
        max_width: "800px";
        margin: "0 auto";
    }
    pub(crate) header {
        font_size: "28px";
    }
    hidden {
        display: "none";
    }
}