* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #f4f6fb;
  font-family: -apple-system, "Apple SD Gothic Neo", "Malgun Gothic", sans-serif;
  color: #1f2430;
}

.card {
  width: 100%;
  max-width: 480px;
  background: #fff;
  border-radius: 16px;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.08);
  padding: 28px 24px;
}

h1 {
  font-size: 20px;
  margin: 0 0 16px;
}

.progress-bar {
  height: 10px;
  background: #e6e9f2;
  border-radius: 6px;
  overflow: hidden;
}

#progress-bar-fill {
  height: 100%;
  width: 0%;
  background: linear-gradient(90deg, #6c8cff, #7ee3c4);
  transition: width 0.3s ease;
}

.progress-text {
  margin-top: 6px;
  font-size: 13px;
  color: #6b7280;
}

.node-info {
  margin-top: 24px;
  font-size: 13px;
  color: #6b7280;
  letter-spacing: 0.02em;
}

.prompt {
  margin-top: 10px;
  font-size: 22px;
  font-weight: 600;
  line-height: 1.4;
  min-height: 60px;
}

.answer-area {
  margin-top: 20px;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.answer-area input[type="text"] {
  flex: 1;
  min-width: 120px;
  padding: 12px 14px;
  font-size: 18px;
  border: 2px solid #e6e9f2;
  border-radius: 10px;
  outline: none;
}

.answer-area input[type="text"]:focus {
  border-color: #6c8cff;
}

.answer-area button {
  padding: 12px 20px;
  font-size: 16px;
  font-weight: 600;
  border: none;
  border-radius: 10px;
  background: #6c8cff;
  color: #fff;
  cursor: pointer;
}

.answer-area button:hover {
  background: #5678ea;
}

.choice-btn {
  flex: 1 1 100%;
  text-align: left;
  background: #f4f6fb !important;
  color: #1f2430 !important;
  border: 2px solid #e6e9f2 !important;
}

.choice-btn:hover {
  border-color: #6c8cff !important;
}

.feedback {
  margin-top: 18px;
  min-height: 24px;
  font-size: 15px;
  line-height: 1.5;
}

.feedback.correct {
  color: #1f9d63;
  font-weight: 600;
}

.feedback.incorrect {
  color: #d9534f;
}

.feedback.mastered {
  color: #b8860b;
}

footer {
  margin-top: 28px;
  text-align: right;
}

.reset-btn {
  background: none;
  border: none;
  color: #9aa1b0;
  font-size: 12px;
  cursor: pointer;
  text-decoration: underline;
}