body {
  margin: 0;
  background: #000;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

#start-button {
  position: absolute;
  z-index: 999;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  padding: 20px 40px;
  font-size: 24px;
  font-family: monospace;
  background: black;
  color: white;
  border: 2px solid white;
  cursor: pointer;
  transition: background 0.3s;
}

#start-button:hover {
  background: #111;
}

#game-container {
  position: relative;
  width: 600px;
  height: 500px;
  background: rgb(9, 9, 14);
  border: 3px solid #444;
  overflow: hidden;
}

#drone {
  width: 40px;
  height: 40px;
  background-image: url('assets/drone_transparent_40x40.gif');
  background-size: cover;
  background-position: center;
  background-repeat: no-repeat;
  position: absolute;
  left: 100px;
  transition: top 0.15s;
  z-index: 10;
}

.wall {
  width: 40px;
  background: green;
  position: absolute;
  right: -40px;
  animation: moveWall 1s linear forwards;
  z-index: 5;
}

#item {
  position: absolute;
  left: 100px;
  font-size: 32px;
  z-index: 15;
}

.hidden {
  display: none;
}

@keyframes moveWall {
  from {
    right: -40px;
  }
  to {
    right: 600px;
  }
}