* { box-sizing: border-box; margin: 0; padding: 0; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang HK", sans-serif;
  background: #e8f5e9;
  color: #222;
  padding: 10px;
  max-width: 420px;
  margin: 0 auto;
  text-align: center;
}
header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 15px; }
h1 { font-size: 1.6rem; }
.big-btn {
  background: #4caf50;
  color: white;
  border: none;
  border-radius: 12px;
  padding: 16px 28px;
  font-size: 1.3rem;
  min-height: 56px;
  cursor: pointer;
  margin: 10px;
}
#canvas {
  background: white;
  border-radius: 16px;
  box-shadow: 0 4px 8px rgba(0,0,0,0.1);
  touch-action: none;
}