h1 {
  /* Set the font-size and line-height while keeping a proper vertical rhythm. */
  font-size: 2em;
  line-height: 1.5em; /* 3rem / 2em = 1.5em */
  /* Set 1 unit of vertical rhythm on the top and bottom margins. */
  margin-top: 0.75em; /* 1.5rem / 2em = .75em */
  margin-bottom: 0.75em;
}
h2 {
  font-size: 1.5em;
  line-height: 2em; /* 3rem / 1.5em = 2em */
  margin-top: 1em; /* 1.5rem / 1.5em = 1em */
  margin-bottom: 1em;
}
h3 {
  font-size: 1.17em;
  line-height: 1.28205em; /* 1.5rem / 1.17em = 1.28205em */
  margin-top: 1.28205em;
  margin-bottom: 1.28205em;
}
h4 {
  font-size: 1em;
  line-height: 1.5em; /* 1.5rem / 1em = 1.5em */
  margin-top: 1.5em;
  margin-bottom: 1.5em;
}
h5 {
  font-size: 0.83em;
  line-height: 1.80723em; /* 1.5rem / 0.83em = 1.80723em */
  margin-top: 1.80723em;
  margin-bottom: 1.80723em;
}
h6 {
  font-size: 0.67em;
  line-height: 2.23881em; /* 1.5rem / 0.67em = 2.23881em */
  margin-top: 2.23881em;
  margin-bottom: 2.23881em;
}