style.css

/* General settings */

@import url('https://fonts.googleapis.com/css2?family=Acme&family=Amatic+SC:wght@700&display=swap');

html {
  box-sizing: border-box;
  background-color: #c3f37b;
  font-family: 'Acme', sans-serif;
}

body {
  margin: 0;
}

/* Panels' settings */

.panels {
  display: flex;
  overflow: hidden;
  height: 100vh;
  cursor: pointer;
}

.panel {
  display: flex;
  justify-content: center;
  flex-direction: column;
  flex: 1;
  text-align: center;
  align-items: center;
  background-size: cover;
  background-position: center;
  box-shadow: inset 0 0 0 .5vmin rgba(196, 195, 195, 0.1);
  color: #fff;
  font-size: 2vmin;
  transition: 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);
}

/* Images for the panels */

.panel01 { background-image: url('img/img-01.jpg'); }
.panel02 { background-image: url('img/img-02.jpg'); }
.panel03 { background-image: url('img/img-03.jpg'); }
.panel04 { background-image: url('img/img-04.jpg'); }
.panel05 { background-image: url('img/img-05.jpg'); }

/* Flex items */

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

/* Text from each panel */

.panel p {
  text-transform: uppercase;
  text-shadow: 0 0 1vmax rgba(0, 0, 0, 0.72), 0 0 1vmax rgba(0, 0, 0, 0.45);
  font-size: 2em;
  user-select: none;
  background-color: rgba(0, 0, 0, 0.45);
}

.panel p:nth-child(2) {
  font-size: 3.7em;
}

.panel.open {
  flex: 5;
  font-size: 2vmax;
}

@media only screen and (max-width: 600px) {
  .panel p {
    font-size: 1.5em;
  }
}