header, main {
    display: flex;
    flex-direction: column;
    align-items: center;
    box-shadow: 0 0 100px purple;
    background: linear-gradient(purple, darkblue);
}

button {
    width: 80px;
}

body {
    background: linear-gradient(purple, darkblue);
    box-shadow: 0 0 999px purple;
}