Responsively center text horizontally and vertically

styles.css

/* source: https://stackoverflow.com/a/45275695/2154867 */
#text_container {
  display: flex;
  justify-content: center;
  align-items: center;
  width: 100%;
  height: 100vh;  }
#text_container p {
  margin: 0;
  color: white;
  font-size: 4rem;
}