html,
body {
  height: 100%;
  background-color: yellow;
  margin-bottom: 0;
  min-height: 30%;
  background-repeat: no-repeat;
  background-position: center;
  -webkit-background-size: cover;
  background-size: cover;
}

body {
  display: flex;
  align-items: center;
}

.jumbotron {
  position: relative;
  top: 50%;
  transform: translateY(-50%);
  opacity: 0.85;
  background-color: grey;
  padding-bottom: 8px;
}