mobilizon/js/src/components/Activity/activity.scss

.activity-item {
  display: flex;
  span.o-icon {
    width: 2em;
    height: 2em;
    box-sizing: border-box;
    border-radius: 50%;
    border: 2px solid;
    z-index: 2;
    flex-shrink: 0;
  }
}