@media screen and (min-width: 600px) {
  ul.instructors-list {
    columns: 2;
  }
}

@media screen and (min-width: 980px) {
  ul.instructors-list {
    columns: 3;
  }
}

@media screen and (min-width: 1200px) {
  ul.instructors-list {
    columns: 4;
  }
}