:root {
  --border: #ddd;
  --accent: #1e4d8c;
  --green: #b5e2b2;
  --yellow: #fff2a1;
  --orange: #ffd1a1;
  --red: #f5a1a1;
  --gray: #e0e0e0;
}

/* Basic body layout */
body {
  font-family: system-ui, sans-serif;
  margin: 0;
  background: #fafafa;
  color: #222;
}

/* Header styling */
header {
  background: #fff;
  border-bottom: 1px solid var(--border);
  padding: 1rem;
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  align-items: center;
}

/* Navigation tabs */
.tab-menu {
  display: flex;
  gap: 0.5rem;
  padding: 0.5rem 1rem;
  background: #fff;
  border-bottom: 1px solid var(--border);
}

.tab-menu button {
  background: var(--accent);
  color: white;
  border: none;
  border-radius: 4px;
  padding: 0.4rem 1rem;
  cursor: pointer;
}

.tab-menu button.active {
  background: #163a66;
}

/* Card grid */
#card-container {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 1rem;
  padding: 1rem;
}

/* Each concept card */
.card {
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 1rem;
  cursor: pointer;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
  overflow-x: auto;
}

.card h2 {
  margin-top: 0;
  color: var(--accent);
  font-size: 1.05rem;
}

.card-content {
  display: none;
  margin-top: 0.5rem;
  overflow-x: auto;
  white-space: normal;
}

.card.open .card-content {
  display: block;
}

/* MathJax equation containment */
mjx-container {
  display: block !important;
  width: fit-content !important;
  max-width: 100% !important;
  white-space: normal !important;
  overflow-x: auto !important;
}

/* Practice section */
#practice-section {
  background: #fff;
  border-top: 2px solid var(--accent);
  margin: 1rem;
  padding: 1rem;
  border-radius: 6px;
}

.practice-container {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  flex-wrap: wrap;
}

.practice-left {
  flex: 3;
  min-width: 260px;
}

.practice-buttons {
  display: flex;
  gap: 0.5rem;
  align-items: center;
  margin-top: 0.5rem;
}

#answerBox {
  flex: 1;
  padding: 0.4rem;
  border: 1px solid var(--border);
  border-radius: 4px;
  min-width: 200px;
  margin-top: 0.5rem;
}

#practiceBtn,
#checkBtn {
  background: var(--accent);
  color: white;
  border: none;
  border-radius: 4px;
  padding: 0.4rem 1rem;
  cursor: pointer;
}

#practice-card {
  margin-top: 1rem;
  border: 1px dashed var(--border);
  padding: 1rem;
  min-height: 100px;
  background: #fdfdfd;
}

.fuzzy {
  filter: blur(5px);
  opacity: 0.6;
}

/* Score panel */
.score-panel {
  flex: 1;
  min-width: 180px;
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 1rem;
  background: #f7f7f7;
}

.score-line {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 0.4rem;
}

.scoreBox {
  width: 70px;
  text-align: center;
  padding: 0.3rem;
  border-radius: 4px;
  background: var(--gray);
}

/* Print layout */
@media print {
  header,
  .tab-menu,
  #practice-section {
    display: none;
  }

  body {
    background: #fff;
  }

  .card {
    page-break-inside: avoid;
    border: 1pt solid #000;
  }
}