body {
  padding-top: 70px;
}

.hero {
  height: 100vh;
  background: linear-gradient(rgba(0,0,0,.6), rgba(0,0,0,.6)),
              url('../images/classroom.jpg') center/cover no-repeat;
}

.hero h1 {
  font-size: 3rem;
}

@media (max-width: 768px) {
  .hero h1 {
    font-size: 2rem;
  }
}