Unless there will be more dialogs very similar to this one, there is no need to use CSS classes here: `#progressToast` should do fine. There is even less need to use classes for the dialog's elements: `#title` is more performant than `span.title`, while being semantically clearer (a class indicates there can be multiple `span.titles`). The same goes for the rest of the elements.

Also, even when using classes, prefixing a class with the element's type is discouraged by Google HTML Style Guide (less maintainable).