/* Use a more-intuitive box-sizing model */
*,
*::before,
*::after {
    box-sizing: border-box;
}

/* Remove default margin */
* {
    margin: 0;
}

body {
    padding: 1em;
}

#controls {
    margin-bottom: 1em;
}

#keyboard {
    position: relative;
}

.key {
    padding: 0.5em;
    border-radius: 0.4rem;
    border: 2px solid transparent;
    background-color: #eee;
    background-clip: padding-box;
    overflow: hidden;
    position: absolute;
    font-size: 60%;
    word-break: break-all;
}

.key.pressed {
    background-color: #ccc;
}

.marker {
    --size: 1rem;
    position: absolute;
    width: var(--size);
    height: var(--size);
    transform: translate(-50%, -50%);
    background: #333;
    opacity: 0.2;
    border-radius: 50%;
}