body{
    display: flex;
    min-height: 100vh;
    align-items: center;
    justify-content: center;
    text-align: center; 
    flex-direction: column;
    overflow: hidden;
}
a.btn{
    font-size: 2.5em;
}

@media(max-width:768px){
    a.btn{
        font-size: 1.2em;
    }
}