:root {
  --bg: #f7f9fc;
  --panel: #ffffff;
  --line: #d7deea;
  --text: #1f2a3a;
  --primary: #2e6de0;
  --primary-dark: #1f52ae;
  --ok: #1a8f4d;
  --ng: #c23333;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Hiragino Kaku Gothic ProN", "Yu Gothic", "Meiryo", sans-serif;
  color: var(--text);
  background: var(--bg);
  line-height: 1.6;
}

.hero {
  background: linear-gradient(120deg, #dbe8ff, #f5f8ff);
  border-bottom: 1px solid var(--line);
  padding: 28px 18px;
  text-align: center;
}

.hero h1 {
  margin: 0 0 8px;
  font-size: 1.9rem;
}

.hero p {
  margin: 0;
}

.container {
  max-width: 980px;
  margin: 0 auto;
  padding: 18px;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 18px;
  margin-bottom: 18px;
}

.panel h2 {
  margin-top: 0;
  border-left: 5px solid var(--primary);
  padding-left: 10px;
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 12px;
}

.card {
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 12px;
  background: #fcfdff;
}

.card h3 {
  margin-top: 0;
  font-size: 1.02rem;
}

.formula {
  font-size: 1.1rem;
  font-weight: 700;
  overflow-wrap: anywhere;
}

.flashcard {
  border: 2px dashed var(--line);
  border-radius: 12px;
  padding: 18px;
  min-height: 130px;
  display: grid;
  align-items: center;
  background: #fafcff;
}

.question {
  font-size: 1.15rem;
  margin: 0;
  font-weight: 700;
}

.answer {
  margin-top: 10px;
  color: var(--primary-dark);
}

.hidden {
  display: none;
}

.actions {
  margin-top: 12px;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

button {
  border: none;
  border-radius: 8px;
  background: var(--primary);
  color: #fff;
  padding: 10px 14px;
  cursor: pointer;
  font-size: 0.95rem;
}

button:hover {
  background: var(--primary-dark);
}

button.secondary {
  background: #67758f;
}

.counter {
  margin-top: 10px;
  color: #55617a;
}

.quiz-item {
  border-top: 1px solid var(--line);
  padding: 12px 0;
}

.quiz-item:first-child {
  border-top: none;
}

.quiz-question {
  margin: 0 0 8px;
  font-weight: 700;
}

.quiz-options {
  display: grid;
  gap: 6px;
}

.quiz-options label {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 7px 10px;
  background: #fff;
}

.result {
  margin-top: 14px;
  border-radius: 8px;
  background: #eef4ff;
  padding: 12px;
}

.result .ok {
  color: var(--ok);
  font-weight: 700;
}

.result .ng {
  color: var(--ng);
  font-weight: 700;
}

.footer {
  text-align: center;
  padding: 6px 10px 18px;
  color: #5f6b80;
}