* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, sans-serif;
  background: #111827;
  color: #f9fafb;
}

.app {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 24px;
}

.card {
  width: 100%;
  max-width: 520px;
  background: #1f2937;
  border-radius: 24px;
  padding: 28px;
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.35);
}

h1 {
  margin: 0;
  font-size: 42px;
  text-align: center;
}

.subtitle {
  margin-top: 6px;
  text-align: center;
  color: #d1d5db;
}

.formula {
  margin: 22px 0;
  padding: 16px;
  background: #374151;
  border-radius: 14px;
  text-align: center;
  font-size: 20px;
  font-weight: bold;
}

.control {
  margin: 20px 0;
}

label {
  display: block;
  margin-bottom: 8px;
  font-weight: bold;
}

input[type="range"] {
  width: 100%;
}

.result {
  margin-top: 26px;
  padding: 18px;
  background: #030712;
  border-radius: 18px;
  text-align: center;
}

.result p {
  margin: 8px 0;
  color: #9ca3af;
}

.result h2 {
  margin: 6px 0 18px;
  font-size: 34px;
}

.buttons {
  display: flex;
  gap: 12px;
  margin-top: 22px;
}

button {
  flex: 1;
  border: none;
  border-radius: 14px;
  padding: 14px;
  font-size: 16px;
  font-weight: bold;
  cursor: pointer;
}

#playButton {
  background: #22c55e;
  color: #052e16;
}

#stopButton {
  background: #ef4444;
  color: #450a0a;
}

.hint {
  margin-top: 18px;
  color: #d1d5db;
  text-align: center;
  font-size: 14px;
}