@keyframes fly {
    0% { transform: translateY(0px); }
    50% { transform: translateY(-5px); }
    100% { transform: translateY(0px); }
}

#bird {
    animation: fly 0.5s infinite ease-in-out;
}

.pipe {
    position: absolute;
    width: 60px;
    background-color: #4ade80;
    border: 3px solid #22c55e;
    border-radius: 5px;
}

.pipe-top {
    top: 0;
}

.pipe-bottom {
    bottom: 0;
}

.ground {
    position: absolute;
    bottom: 0;
    width: 100%;
    height: 20px;
    background-color: #a16207;
    z-index: 5;
}