* {
  box-sizing: border-box;
  padding: 0;
  margin: 0;
}
body {
  font-family: sans-serif;
}
header {
  background: rgb(52, 206, 142);
  height: 100px;
}
h1 {
  color: white;
  text-align: center;
  line-height: 100px;

}
article {
  background: rgba(16, 233, 215, 0.178);
  padding: 10px;
  margin: 10px;
}
.group-a {
  display: flex;
  flex-direction: row;
}
.group-b {
  display: flex;
  flex-direction: row-reverse;
}
.group-c {
  display: flex;
  flex-direction: column-reverse;
}
.group-d {
  display: flex;
  flex-direction: column;
}
.group-e {
  display: flex;
  flex-direction: row;
  flex-basis: 50%;
}
.group-f {
  display: flex;
  flex-direction: row;
  flex-basis: 50%;
}