.symbol {
  position: absolute;
  font-weight: bold;
  opacity: 0;
  animation: fadeInOut 6s ease-in-out infinite;
  pointer-events: none; /* opcional: no interfiere con el mouse */
}

@keyframes fadeInOut {
  0%   { opacity: 0; }
  20%  { opacity: 1; }
  80%  { opacity: 1; }
  100% { opacity: 0; }
}
#zona-de-animacion {
  position: relative;
  width: 100%;
  height: auto;
  overflow: hidden;
}

#rect-container {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  z-index: 1;
  background: transparent;
}

.container {
  position: relative;
  z-index: 2;
}