Hey @julienw can you think of something more elegant here? It would be great if we don't touch js at all for such styling. But as ```light``` class name is provided by BB and have more than one style block associated with it we shouldn't override it like this:

```
.incoming {
  progress {
    background-image: url(..._path_to_light_spinner)
  }
}
```

Only LESS\SASS-like syntax that we don't support comes in mind :)

```
.incoming {
  progress {
    &.bb-progress-light;
  }
}

.outgoing {
  progress {
    &.bb-progress-dark;
  }
}
```

I'm just thinking about removing JS dependency for guys who mainly work with CSS only. Or maybe Web Components initiative will help somehow here and I don't need to bother about it :)