.post-navigation {
  display: flex;
  justify-content: space-between;
  align-items: center;

  /* Try larger margins to test */
  margin: 70px 70px;   /* top/bottom: 70px, left/right: 70px */
  padding: 100px 0;

  border-top: 1px solid #ddd;
  border-bottom: 1px solid #ddd;
}

.post-navigation a {
  text-decoration: none;
  color: #2962ff;
  font-weight: 600;
}

.post-navigation a:hover {
  text-decoration: underline;
}

/* align sides */
.nav-previous {
  margin-right: auto;
  text-align: left;
}

.nav-next {
  margin-left: auto;
  text-align: right;
}