style.css

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

.game-board {
    width: 100%;
    height: 500px;
    border-bottom: 15px solid rgb(35, 160, 35);
    margin: 0 auto;
    position: relative;
    overflow: hidden;
    background: linear-gradient(#87ceeb, #e0f6ff);
}

.pipe {
    position: absolute;
    bottom: 0;
    width: 80px;
    animation: pipe-animation 2.8s infinite linear;
}

@keyframes pipe-animation {
    from {
        right: -80px;
    }
    to {
        right: 100%;
    }
}

.mario {
    width: 150px;
    position: absolute;
    bottom: 0px;
}

.jump {
    animation: jump 700ms ease-out;
}

@keyframes jump {
    0% {bottom: 0;}
    30% {bottom: 150px;}
    40% {bottom: 170px;}
    50% {bottom: 180px;}
    60% {bottom: 170px;}
    70% {bottom: 150px;}
    100% {bottom: 0;}
}

.clouds {
    position: absolute;
    width: 550px;
    animation: clouds-animation 15s infinite linear;
}

@keyframes clouds-animation {
    from {
        right: -550px;
    }
    to {
        right: 100%;
    }
}