html, body {
    background-image: url(img/background.png);
    width: 100%;
    height: 100%;
    margin: 0;
    background-size: cover;
    background-position: center;
    overflow: hidden;
    image-rendering: crisp-edges;
    image-rendering: optimizeSpeed;
}
.balloon {
    background-image: url(img/balloon.png);
    background-position: 377px 8px;
    width: 86px;
    height: 100px;
    position: absolute;
    transition: top 2s, left 2s;
}
.balloon.pop {
    background-position: 257px -85px;
}