@adobe/spectrum-css/dist/components/quickaction/multiStops/darkest.css

The Spectrum CSS top-level backwards compatible package

.spectrum--darkest .spectrum-QuickActions-overlay {
  background-color: rgba(0,0,0,0.2);
}
.spectrum--darkest .spectrum-QuickActions {
  background-color: rgba(30,30,30,0.9);
}