w3-display-middle{
  font-size: xlarge
}
header, h1, h2, h3, h4, h5, h6 {
  font-size: xlarge
}
body, h1, h2, h3, h4, h5, h6 {
  font-size: xlarge}

.container {
  height: 600px;
  position: relative;
  border: 3px solid green;
}

.center {
  margin: 0;
  position: absolute;
  top: 70%;
  left: 50%;
  -ms-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
}