header {
  -js-display: flex;
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-pack: justify;
  -webkit-justify-content: space-between;
  -ms-flex-pack: justify;
  justify-content: space-between;
  padding: 10px;
}

ul {
  -js-display: flex;
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -webkit-align-items: center;
  -ms-flex-align: center;
  align-items: center;
}

ul li {
  margin-left: 5px;
  margin-right: 5px;
}

main {
  -js-display: flex;
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-flex-wrap: wrap;
  -ms-flex-wrap: wrap;
  flex-wrap: wrap;
  padding: 10px;
}

main div.animal {
  width: calc(33.3% - 10px);
  margin: 5px;
}


@media (max-width: 500px) {
  header {
    -webkit-box-orient: vertical;
    -webkit-box-direction: normal;
    -webkit-flex-direction: column;
    -ms-flex-direction: column;
    flex-direction: column;
    -webkit-box-align: center;
    -webkit-align-items: center;
    -ms-flex-align: center;
    -ms-grid-row-align: center;
    align-items: center;
  }

  main div.animal {
    width: calc(50% - 10px);
    margin: 5px;
  }
}