style.css

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

.game-board {
  width: 100%;
  height: 500px;
  border-bottom: 15px solid green;
  margin: 0 auto;
  position: relative;
  background: linear-gradient(#87CEEB, #E0F6FF);
  overflow: hidden;
}

.pipe {
  position: absolute;
  bottom: 0;
  width: 80px;
  animation: pipe-animation 2s infinite linear;
}

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

.jump {
  animation: jump 500ms infinite ease-out;  
}

.cloud {
  position: absolute;
  top: 10px;
  width: 450px;
  animation: cloud-animation 20s infinite linear;
}

.score {
  position: absolute;    
  font-family: 'Press Start 2P', cursive;
  text-align: center;
  padding: 10px;
  font-size: 2em;
  color: #FFD700;
  text-shadow: 2px 2px 4px #000000;
}

#gameOver {
  display: none;
  max-width: 100%;
  max-height: 80vh;
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

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

  to {
    right: 100%;
  }
}

@keyframes jump {
  0% {
    bottom: 0;
  }

  40% {
    bottom: 180px;
  }

  50% {
    bottom: 180px;
  }

  60% {
    bottom: 180px;
  }

  100% {
    bottom: 0;
  }
}

@keyframes cloud-animation {
  from {
    right: -450px;
  }
    
  to {
    right: 100%;    
  }
}