style.css

body {
    display: block;
    background: #fafafa;
}
header,footer,.gameOver,.scoreDisplay {
    font-family: 'Press Start 2P', cursive;
    color: #666666;
}
header,footer {
    background-color: #AAAAAA;
    color: #ffffff;
    position: absolute;
    width: 100%;
    text-align: center;
}
footer {
    bottom: 0;
}
.ring {
    width: 30;
    height: 30;
}
.dino {
    position: absolute;
    width: 52px;
    height: 60px;
    background-image: url(img/sonic-run2.gif);
    bottom: 0;
}

.gameOver {
    text-align: center;
    padding-bottom: 120px;
}
.scoreDisplay {
    text-align: right;
    margin-right: 100px;
}

.cactus {
    position: absolute;
    width: 60px;
    height: 60px;
    bottom: 0;
    background-image: url(img/cactus.png);
}

/*animação*/

@keyframes slideright {
    from {
        background-position: 7000%;
    }
    to {
        background-position: 0;
    }
}

.background {
    position: absolute;
    bottom: 50%;
    background-image: url(img/background.png);
    background-repeat: repeat-x;
    animation: slideright 800s linear;
    animation-iteration-count: infinite;
    width: 100%;
    height: 200px;
}