#container {
    display: flex;           /* establish flex container */
    flex-direction: column;  /* make main axis vertical */
    justify-content: center; /* center items vertically, in this case */
    align-items: center;     /* center items horizontally, in this case */
    height: 300px;
}

.hier2 {
  text-align: center;
  max-width: 500px;
  margin-top: 100px;
  margin-bottom: 100px;
  margin-right: auto;
  margin-left: auto;
  padding: 10px;
  font-family: arial;
  font-size: 1.0rem;
  color: #fff;
  border: 3px solid #73AD21;
  background: #003366;
}