my css on a component:

:host .foo .bar {
  color: red;
}

.foo .bar {
  color: green;
}

it gets translated into:

[_nghost-shh-2] .foo .bar {
  color: red;
}

.foo[_ngcontent-shh-2] .bar[_ngcontent-shh-2] {
  color: green;
}

it is a great missing feature if this is indeed working as intended - but on the first look it seems like a bug to not shim add the shimmed attribute onto classes after :host.