* { box-sizing: border-box; margin: 0; padding: 0; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang HK", sans-serif;
  background: #f1f8e9;
  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, .shape {
  background: #8bc34a;
  color: white;
  border: none;
  border-radius: 12px;
  padding: 16px 24px;
  font-size: 2rem;
  min-height: 60px;
  cursor: pointer;
  margin: 8px;
}
#paper { font-size: 4rem; min-height: 150px; background: white; border-radius: 16px; margin: 20px 0; padding: 20px; border: 3px solid #c5e1a5; }