body {
  text-align: center;
  font-family: Arial, sans-serif;
  background: #222;
  color: #fff;
}

h1 {
  margin-top: 20px;
}

#startBtn {
  margin: 20px;
  padding: 10px 20px;
  font-size: 16px;
  border-radius: 10px;
  cursor: pointer;
}

.game-board {
  display: grid;
  grid-template-columns: repeat(2, 150px);
  grid-template-rows: repeat(2, 150px);
  gap: 10px;
  justify-content: center;
  margin-top: 20px;
}

.pad {
  border-radius: 20px;
  cursor: pointer;
  transition: background 0.3s, box-shadow 0.3s;
}

/* Base colors */
.red    { background: darkred; }
.green  { background: darkgreen; }
.blue   { background: darkblue; }
.yellow { background: goldenrod; }

/* Flash effect (lighter inside glow) */
.red.active {
  background: red;
  box-shadow: inset 0 0 30px #ff6666, 0 0 20px #fff;
}
.green.active {
  background: limegreen;
  box-shadow: inset 0 0 30px #66ff66, 0 0 20px #fff;
}
.blue.active {
  background: dodgerblue;
  box-shadow: inset 0 0 30px #66ccff, 0 0 20px #fff;
}
.yellow.active {
  background: yellow;
  box-shadow: inset 0 0 30px #ffff99, 0 0 20px #fff;
}

footer {
  margin-top: 30px;
  font-size: 18px;
  color: #ddd;
}