/* Global */

html {
  box-sizing: border-box;
  background: gainsboro;
  font-family: 'helvetica neue';
  font-size: 20px;
  font-weight: 200;
}

body {
  margin: 0;
}

*, *:before, *:after {
  box-sizing: inherit;
}

.panels {
  overflow: hidden;
  display: flex;
}

.panel {
  background: gainsboro;
  box-shadow: inset 0 0 0 5px rgba(255,255,255,0.1);
  color: white;
  text-align: center;
  /* Safari transitionend event.propertyName === flex */
  /* Chrome + FF transitionend event.propertyName === flex-grow */
  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;
  font-size: 20px;
  background-size: cover;
  background-position: center;
  flex: 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items:center;
}

.panel > * {
  transition: transform 0.5s;
}

.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);
  }

.button {
  padding: 15px 40px;
  border-radius: 40px;
  font-size: 18px;
  color: indianred;
  font-family: 'Quicksand', sans-serif;
  cursor: pointer;
  transition: background-color 0.3s ease;
}

.button:focus {
  outline: thin dotted;
}

.button:hover {
  background-color: rgba(256, 256, 256, 1)
}

.button4 {
  border: 2px solid indianred;
  background-color: rgba(256, 256, 256, 0.9);
}

/* Vertical layout */
@media (max-width: 767px) {
  .panels {
    height: 100vh;
    flex-direction: column;
  }

  .panel {
    overflow: hidden;
  }

  .panel1 { background-image:url(https://source.unsplash.com/hv1MrBzGGNY/800x800); }
  .panel2 { background-image:url(https://source.unsplash.com/ycVFts5Ma4s/800x800); }
  .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=800&h=800&fit=crop&s=967e8a713a4e395260793fc8c802901d); }
  .panel4 { background-image:url(https://source.unsplash.com/o7BP1GRKk1s/800x800); }

  .panel > * {
    margin: 0;
    flex: 1;
  }

  .panel p {
    font-size: 2em;
  }

  .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.open {
    font-size: 40px;
    flex: 4;
  }

}


/* Horizontal layout */
@media (min-width: 768px) {
  .panels {
    min-height: 100vh;
  }

  .panel1 { background-image:url(https://source.unsplash.com/hv1MrBzGGNY/1500x1500); }
  .panel2 { background-image:url(https://source.unsplash.com/ycVFts5Ma4s/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/o7BP1GRKk1s/1500x1500); }

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

  .panel p {
    font-size: 2em;
  }

  .panel p:nth-child(2) {
    font-size: 4em;
  }

  .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.open {
    font-size: 40px;
    flex: 4;
  }
}