h1 {
    background: #4a90e2;
    color: #fff;
    padding: 15px;
    border-radius: 5px;
    text-align: center;
}

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

.back {
    display: inline-block;
    margin-top: 20px;
    text-decoration: none;
    color: #555;
}

body.dark .back {
    color: #999;
}

body.dark .back:hover {
    color: #fff;
}
.back:hover { color: #000; }