html, body {
 height: 100%;
}

.panel {
 position: fixed;
 width: 100%;
 height: 100%;
 top: 0;
 left: 0;
 text-align: center
}

section:not(.first) {
 opacity: 0;
 visibility: hidden;
 transform: scale(0.8);
} 

.panel p {
 font-size: 5vw;
}