html {
  box-sizing: border-box;
}

.panels {
  min-height: 100vh;
  overflow: hidden;
  display: flex;
  font-size: 20px;
  font-weight: 200;
}

.panel {
  text-align: center;
  align-items: center;
  background-size: cover;
  background-position: center;
  flex: 1;
  color: white;
  justify-content: center;
  align-items: center;
  display: flex;
  flex-direction: column;
  transition:
  font-size 0.7s cubic-bezier(0.61,-0.19, 0.7,-0.11),
  flex 0.7s cubic-bezier(0.61,-0.19, 0.7,-0.11),
  background 0.2s;
}

.panel1 {
  background-image: url(https://source.unsplash.com/gYl-UtwNg_I/1500x1500);
}
.panel2 {
  background-image: url(https://source.unsplash.com/rFKUFzjPYiQ/1500x1500);
}
.panel3 {
  background-image: url(https://images.unsplash.com/photo-1465188162913-8fb5709d6d57?ixlib=rb-0.3.5&q=80&fm=jpg&crop=faces&cs=tinysrgb&w=1500&h=1500&fit=crop&s=967e8a713a4e395260793fc8c802901d);
}
.panel4 {
  background-image: url(https://source.unsplash.com/ITjiVXcwVng/1500x1500);
}
.panel5 {
  background-image: url(https://source.unsplash.com/3MNzGlQM7qs/1500x1500);
}

.panel > * {
    margin: 0;
    width: 100%;
    flex: 1 0 auto;
    display: flex;
    justify-content: center;
    align-items: center;
    transition: transform 0.5s;
    
  }

  .panel > *:first-child{ transform: translateY(-100%);}
  .panel.open-active > *:first-child{ transform: translateY(0);}
  .panel > *:last-child{ transform: translateY(100%);}
  .panel.open-active > *:last-child{ transform: translateY(0);}

  .panel p {
    text-transform: uppercase;
    font-family: 'Amatic SC', cursive;
    text-shadow: 0 0 4px rgba(0, 0, 0, 0.72), 0 0 14px rgba(0, 0, 0, 0.45);
    font-size: 2em;
  } 

  .panel.open{
    flex: 5;
    font-size: 48px;
  }