#matrix-background {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: -1;         /* behind all content */
  pointer-events: none; /* clicks pass through */
  background-color: #000;
opacity:0.2;
  display: block;
}
#matrix-mute-btn {
  position: fixed;
  bottom: 10px;
  right: 10px;
  z-index: 1000;
  background: transparent;
  border: none;
  color: #0F0;
  font-size: 24px;
  cursor: pointer;
  padding: 4px;
}