html, body {
    margin: 0;
    padding: 0;
    height: 100vh;
    width: 100%;
}

header {
    width: 100%;
    height: 100%;
    margin: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: #eee;
}

h1 {
    margin: 0;
    text-align: center;
    width: 100%;
}