css/style.css

table {
    border-collapse: collapse;
}

#chord {
    margin: 0 auto;
    display: block;
}

a {
    text-decoration: none;
    display: block;
    float: right;
}

#demo {
    display: contents;
}

select {
    width: 100%;
}

iframe {
    width: 100%;
    aspect-ratio: 16/9;
}

#maintab {
    margin: 0 auto;
}