body {
  display: flex;
  justify-content: center;  /* centraliza na horizontal */
  align-items: center;      /* centraliza na vertical */
  height: 100vh;            /* ocupa toda a altura da janela */
  margin: 0;                /* remove margens padrão */
  background-color: #000;   /* cor de fundo opcional */
}

#game-container {
  display: flex;
  justify-content: center;
  align-items: center;
}