We currently have `@embed` which embeds the data inside the stylesheet. While this seems fine for critical-style images, we should consider providing an alternative for non-critical images.
* `@push` annotation - would make use of HTTP/2 server push.
- `@preload` annotation - would add the url in a preload link header.
The problem with non-critical images is that removing embedding without an alternative, plain delivery has the problem of being discovered late and requires additional roundtrips at a point in time when the browser is supposed to render it immediately. (e.g. `:hover`, `:active`, class changes, creating new elements, opening dialogs, etc.)