teaser.css in Open Social 8

.teaser__teaser-type {
  background-color: #adadad;
  border-radius: 0 0 8px 8px;
}

.teaser__teaser-type-icon {
  fill: white;
}

@media (min-width: 600px) {
  .teaser__image {
    border-top-left-radius: inherit;
    border-bottom-left-radius: inherit;
    background: #e6e6e6;
  }
  .teaser__teaser-type {
    background-color: rgba(0, 0, 0, 0.5);
    border-radius: 0 0 10px 0;
  }
}