index.css

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

body {
    user-select: none;
    display: flex;
    flex-direction: column;
}

.game {
    flex-grow: 1;
    overflow: hidden;
}

.bar {
    width: 100%;
    height: 40px;
    bottom: 0;
    display: flex;
    align-items: center;
    padding: 0 16px;
}

.mobile .bar {
    justify-content: center;
}

.button {
    border: 0;
    width: 28px;
    height: 28px;
    margin-right: 16px;
    background-size: cover;
    cursor: pointer;
    background-color: #fff;
}

.button__start {
    background-image: url(icons/play.svg);
}

.button__stop {
    background-image: url(icons/pause.svg);
}

.button__random {
    background-image: url(icons/random.svg);
}

.button__clear {
    background-image: url(icons/trash.svg);
}