Template:ColumnGroup/style.css

.solar-columngroup__container {
  display: flex;
  flex-direction: row;
}

.solar-columngroup__column {
  flex: 1;
  min-width: 250px;
}


.solar-columngroup__column:not(:last-child) {
  margin-right: 8px;
}

.solar-columngroup__column .mw-heading {
  border-bottom: none;
}

@media (max-width: 700px) {
  .solar-columngroup__container {
    flex-direction: column;
  }
}