body {
  text-align: center;
  font-family: Arial, sans-serif;
  background: #222;
  color: white;
  transition: background 0.3s;
}

#game-container {
  display: grid;
  grid-template-columns: 150px 150px;
  grid-gap: 15px;
  justify-content: center;
  margin-top: 40px;
}

.btn {
  width: 150px;
  height: 150px;
  border-radius: 20px;
  opacity: 0.8;
  cursor: pointer;
  transition: opacity 0.2s, transform 0.2s;
  box-shadow: 0 0 15px rgba(255,255,255,0.1);
}

.green { background: green; }
.red { background: red; }
.yellow { background: gold; }
.blue { background: blue; }

.btn.active {
  opacity: 1;
  box-shadow: 0 0 20px white;
}

body.game-over {
  background: #8b0000;
}