body {
    font-family: sans-serif;
}

.hidden {
    display: none;
}

#card {
    border: 2px solid gray;
    border-radius: 0.5em;
    padding: 1em;
    display: flex;
    align-items: center;
    color: black;
    background: #ddd;
    width: 20em;
    height: 10em;
    max-width: 100%;
    box-sizing: border-box;
    vertical-align: middle;
}

#card.back {
    color: white;
    background: #333;
}

#card.hidden {
    display: none;
}

#controls {
    padding: 0.2em;
}

.nav-button {
    font-size: 2em;
}