@adobe/spectrum-css/dist/components/banner/index-lg.css

The Spectrum CSS top-level backwards compatible package

.spectrum-Banner {
  display: inline-block;
  border-radius: 8px;
  padding: 4px 8px;
  font-size: 15px;
  line-height: 1.3;
}
.spectrum-Banner-header {
  font-weight: bold;
}
.spectrum-Banner--corner {
  position: absolute;
  top: -10px;
  right: -10px;
}