body {
  background: black;
  color: white;
  text-align: center;
  font-family: sans-serif;
}

#game-container {
  position: relative;
  width: 300px;
  height: 300px;
  margin: 10px auto;
  border: 2px solid white;
}

#game {
  display: grid;
  grid-template-columns: repeat(15, 20px);
  width: 300px;
  height: 300px;
}

.cell {
  width: 20px;
  height: 20px;
  box-sizing: border-box;
}

.invader {
  background-image: url('space-invaders.png'); /* 任意のインベーダー画像を指定 */
  background-size: cover;
}

.shooter {
  background-image: url('canon.png'); /* 任意のインベーダー画像を指定 */
  background-size: cover;
}

.laser {
  background-color: yellow;
}

.enemy-laser {
  background-color: orange;
}

#message {
  position: absolute;
  top: 40%;
  width: 100%;
  color: white;
  font-size: 20px;
  background: rgba(0,0,0,0.6);
  padding: 10px;
  display: none;
}

#scoreboard {
  margin-top: 10px;
}