* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang HK", sans-serif; background: #fff8e1; 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: 20px; }
h1 { font-size: 1.6rem; }
.big-btn { background: #ffc107; color: #333; border: none; border-radius: 12px; padding: 16px 28px; font-size: 1.3rem; min-height: 56px; cursor: pointer; }
#eq { font-size: 2.5rem; background: white; border-radius: 20px; padding: 30px; margin: 30px 0; border: 4px solid #ffe082; font-family: monospace; white-space: pre; }