html {
  --speed: 3s;
  --bird-size: 50px;
  --frame-size: 500px;
}

body {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  font-family: 'Courier New', Courier, monospace;
}

.game {
  position: relative;
  width: calc((var(--frame-size) * 3) / 5);
  height: var(--frame-size);
  background-image: url(/flappy-bird-starter/assets/bg.png);
  background-size: cover;
  background-repeat: no-repeat;
  border: 5px solid black;
  border-radius: 5px;
  overflow: hidden;
}

.bird {
  position: absolute;
  top: 50%;
  width: var(--bird-size);
  transition: top 100ms linear;
}

.pipe {
  position: absolute;
  left: 100%;
  top: 0;
  width: calc(var(--frame-size) / 10);
  height: 40%;
  background-image: url(/flappy-bird-starter/assets/pipe.png);
  background-size: cover;
  background-repeat: no-repeat;
  transform: rotate(180deg);
}

.pipe:nth-child(2) {
  height: 35%;
  top: calc(40% + 25%);
  transform: rotate(360deg);
}

.obstacles {
  animation: move var(--speed) linear infinite;
}

.score {
  position: absolute;
  top: 5px;
  left: 5px;
  z-index: 2;
}

@keyframes move {
  0% {
    left: 100%;
  }
  100% {
    left: -50px;
  }
}