body {
  font: 16px Arial, sans-serif;
  background: #f7f7f7;
  color: #222;
  margin: 0;
}
.card {
  max-width: 390px;
  margin: 8vh auto;
  padding: 28px;
  background: white;
  border: 1px solid #ddd;
  border-radius: 12px;
  box-sizing: border-box;
}
h1 { font-size: 23px; margin: 0 0 12px; }
p { line-height: 1.5; color: #555; }
[hidden] { display: none !important; }
label { display: block; margin: 22px 0 8px; font-weight: bold; }
input {
  box-sizing: border-box;
  width: 100%;
  padding: 13px;
  border: 1px solid #999;
  border-radius: 7px;
  font-size: 23px;
  letter-spacing: 7px;
  text-align: center;
}
button {
  width: 100%;
  margin-top: 14px;
  padding: 13px;
  border: 0;
  border-radius: 7px;
  background: #ff7900;
  color: #000;
  font-weight: bold;
  cursor: pointer;
}
button:disabled { opacity: .45; cursor: default; }
#stop { background: #333; color: white; }
#status { font-size: 14px; min-height: 24px; margin-top: 16px; }
small { display: block; color: #666; margin-top: 20px; line-height: 1.4; }