html, body {
    height: 100%;
}

body {
    font-size: 10vw;
    font-family: Arial;
    display: flex;
    justify-content: center;
    align-items: center;
}

body.running {
    background: lightgreen;
}

main {
    width:75%;
}

button {
    font-size:0.5em;
    padding:1em;
    border-radius: 0.5em;
    color:white;
}

h1 {
    text-align: center;
}

.btn-primary {
    background: blue;
}

.btn-primary:disabled {
    background: lightblue;
}

.btn-secondary {
    background: grey;
}

.btn-secondary:disabled {
    background: darkgrey;
}

.btn-danger {
    background: red;
}
.btn-danger:disabled {
    background: lightpink;
}