mdToast: improve UX to support theme colors and multi-toasts to show

[ThomasBurleson]

See Oh Snap! for comparative UX:

[ThomasBurleson]

@joeyperson - This seems like an entirely reasonable and useful UX; especially for desktop experiences.

[aniforprez]

This is what I wondered when reading the material design specs. A single toast popping up and being replaced by another is perfectly valid UX on mobile because the user doesn't want to be overwhelmed by a line of toasts blocking their view.

But on desktops with ample space and screen real estate, to restrict the developer to a single toast whose information is hidden by another isn't really necessary.

[joeyperson]

Having a distinct color makes total sense, especially as dark designs would not work well with a dark toast with little contrast.

Re: multi-toasts, I think the idea is to keep toasts to a single event at a time, as there may be actions that are available for them, and could fade out of view before reading them all. If many messages are needed, I'd imagine using a different pattern that could include a list of alerts.

[adrianandreias]

Yup, otherwise every project would define the red error message and the green success message.