html, body {
    box-sizing: border-box;
    margin: 0;
    height: 100vh;
    width: 100vw;
}

#container {
    display: flex;
    flex-flow: column;
    height: 100%;
    width: 100%;
}

#menu {
    background-color: black;
    flex: 0 1 auto;
    position: sticky;
    top: 0;
    display: flex;
    padding: 10px;
    gap: 10px;
    z-index: 100;
    margin-bottom: 10px;
}

#menu a {
    display: contents;
}

#menu button {
    flex: 1 1;
    height: 4em;
}

#menu button.selected {
    background-color: yellow;
    border-color: gold;
}

main {
    margin: 0 10px;
}