body {
  font-family: system-ui, sans-serif;
  background: #f4f4f4;
  margin: 0;
}

.app {
  max-width: 420px;
  margin: auto;
  background: #fff;
  padding: 20px;
  min-height: 100vh;
}

h1 {
  text-align: center;
  color: #25D366;
}

.file-box {
  display: block;
  background: #25D366;
  color: #fff;
  text-align: center;
  padding: 14px;
  border-radius: 8px;
  margin-bottom: 15px;
  cursor: pointer;
}

.file-box input {
  display: none;
}

button {
  width: 100%;
  padding: 14px;
  margin-top: 10px;
  border: none;
  border-radius: 8px;
  font-size: 16px;
}

#btnStart {
  background: #2196F3;
  color: white;
}

#btnNext {
  background: #4CAF50;
  color: white;
}

button:disabled {
  opacity: 0.5;
}

.info {
  margin-top: 10px;
  font-size: 14px;
}

.note {
  margin-top: 20px;
  font-size: 13px;
  color: #555;
}