:root {
  --bg-gcs-accent: #0a66c2;
  --bg-gcs-accent-soft: rgba(10, 102, 194, 0.10);
  --bg-gcs-text: #0f172a;
  --bg-gcs-muted: #64748b;
  --bg-gcs-border: rgba(15, 23, 42, 0.12);
  --bg-gcs-card: #ffffff;
  --bg-gcs-radius: 18px;
  --bg-gcs-shadow: 0 18px 45px rgba(15, 23, 42, 0.09);
}

.bg-gcs-block {
  box-sizing: border-box;
  margin: 22px 0;
  color: var(--bg-gcs-text);
  font-family: inherit;
}

.bg-gcs-block *,
.bg-gcs-block *::before,
.bg-gcs-block *::after {
  box-sizing: border-box;
}

.bg-gcs-rule,
.bg-gcs-formula,
.bg-gcs-example,
.bg-gcs-correct-wrong,
.bg-gcs-mistake,
.bg-gcs-compare,
.bg-gcs-timeline,
.bg-gcs-practice,
.bg-gcs-reveal,
.bg-gcs-summary,
.bg-gcs-pattern {
  border: 1px solid var(--bg-gcs-border);
  border-radius: var(--bg-gcs-radius);
  background: var(--bg-gcs-card);
  box-shadow: var(--bg-gcs-shadow);
  padding: 18px;
  overflow: hidden;
}

.bg-gcs-style-minimal {
  box-shadow: none;
  border-radius: 12px;
}

.bg-gcs-style-modern {
  background: linear-gradient(145deg, #ffffff, #f8fbff);
}

.bg-gcs-style-soft-blue {
  background: linear-gradient(145deg, #ffffff, #f5f9ff);
  border-color: rgba(10, 102, 194, 0.20);
}

.bg-gcs-style-academic {
  border-left: 5px solid var(--bg-gcs-accent);
  border-radius: 12px;
}

.bg-gcs-style-card {
  box-shadow: 0 12px 28px rgba(15, 23, 42, 0.08);
}

.bg-gcs-head {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 12px;
  color: var(--bg-gcs-text);
}

.bg-gcs-head strong {
  font-size: 16px;
  line-height: 1.3;
}

.bg-gcs-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 30px;
  height: 30px;
  min-width: 30px;
  border-radius: 999px;
  background: var(--bg-gcs-accent-soft);
  color: var(--bg-gcs-accent);
  font-weight: 900;
  font-size: 14px;
}

.bg-gcs-body p:last-child,
.bg-gcs-note p:last-child {
  margin-bottom: 0;
}

.bg-gcs-body p:first-child {
  margin-top: 0;
}

.bg-gcs-rule-tip .bg-gcs-icon { background: rgba(34, 197, 94, 0.14); color: #15803d; }
.bg-gcs-rule-warning .bg-gcs-icon,
.bg-gcs-mistake .bg-gcs-icon { background: rgba(245, 158, 11, 0.16); color: #b45309; }
.bg-gcs-rule-note .bg-gcs-icon { background: rgba(99, 102, 241, 0.14); color: #4f46e5; }

.bg-gcs-table-wrap {
  overflow-x: auto;
  border: 1px solid rgba(15, 23, 42, 0.10);
  border-radius: 14px;
}

.bg-gcs-table {
  width: 100%;
  border-collapse: collapse;
  margin: 0;
  font-size: 14px;
}

.bg-gcs-table th {
  background: var(--bg-gcs-accent-soft);
  color: var(--bg-gcs-text);
  text-align: left;
  font-weight: 800;
}

.bg-gcs-table th,
.bg-gcs-table td {
  padding: 12px 14px;
  border-bottom: 1px solid rgba(15, 23, 42, 0.08);
  vertical-align: top;
}

.bg-gcs-table tr:last-child td {
  border-bottom: 0;
}

.bg-gcs-table code,
.bg-gcs-pattern-item code {
  background: rgba(15, 23, 42, 0.06);
  border-radius: 8px;
  padding: 3px 7px;
  color: var(--bg-gcs-text);
}

.bg-gcs-correct-wrong {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}

.bg-gcs-wrong,
.bg-gcs-correct {
  border-radius: 14px;
  padding: 14px;
}

.bg-gcs-wrong {
  background: rgba(239, 68, 68, 0.08);
  border: 1px solid rgba(239, 68, 68, 0.22);
}

.bg-gcs-correct {
  background: rgba(34, 197, 94, 0.09);
  border: 1px solid rgba(34, 197, 94, 0.24);
}

.bg-gcs-wrong p,
.bg-gcs-correct p {
  margin: 8px 0 0;
}

.bg-gcs-label,
.bg-gcs-mini-label {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  font-weight: 800;
  font-size: 13px;
}

.bg-gcs-label-wrong { color: #dc2626; }
.bg-gcs-label-correct { color: #16a34a; }

.bg-gcs-note {
  grid-column: 1 / -1;
  padding: 12px 14px;
  border-radius: 14px;
  background: rgba(10, 102, 194, 0.08);
  color: #334155;
  font-size: 14px;
}

.bg-gcs-mini-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin-bottom: 10px;
}

.bg-gcs-mini-grid > div {
  padding: 12px;
  border-radius: 12px;
  background: rgba(15, 23, 42, 0.04);
}

.bg-gcs-compare-grid,
.bg-gcs-pattern-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 14px;
}

.bg-gcs-compare-item,
.bg-gcs-pattern-item {
  padding: 15px;
  border: 1px solid rgba(15, 23, 42, 0.10);
  border-radius: 14px;
  background: rgba(255, 255, 255, 0.72);
}

.bg-gcs-compare-item h4 {
  margin: 0 0 8px;
  color: var(--bg-gcs-accent);
}

.bg-gcs-compare-item p:last-child {
  margin-bottom: 0;
}

.bg-gcs-pattern-item {
  display: grid;
  gap: 8px;
}

.bg-gcs-pattern-item strong {
  font-size: 16px;
  color: var(--bg-gcs-accent);
}

.bg-gcs-pattern-item em {
  color: var(--bg-gcs-muted);
}

.bg-gcs-timeline-label {
  text-align: center;
  font-weight: 800;
  margin: 6px 0 14px;
}

.bg-gcs-line {
  position: relative;
  height: 34px;
  margin: 0 16px;
}

.bg-gcs-line::before {
  content: "";
  position: absolute;
  top: 16px;
  left: 0;
  right: 0;
  height: 4px;
  border-radius: 999px;
  background: linear-gradient(90deg, var(--bg-gcs-accent), rgba(10,102,194,0.55));
}

.bg-gcs-dot {
  position: absolute;
  top: 9px;
  width: 18px;
  height: 18px;
  border: 3px solid #fff;
  border-radius: 999px;
  background: var(--bg-gcs-accent);
  box-shadow: 0 0 0 2px rgba(10,102,194,0.20);
  z-index: 2;
}

.bg-gcs-dot-start { left: 0; }
.bg-gcs-dot-mid { left: calc(50% - 9px); }
.bg-gcs-dot-now { right: 0; }
.bg-gcs-arrow {
  position: absolute;
  top: 10px;
  right: -6px;
  width: 0;
  height: 0;
  border-top: 10px solid transparent;
  border-bottom: 10px solid transparent;
  border-left: 12px solid var(--bg-gcs-accent);
}

.bg-gcs-timeline-captions {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  text-align: center;
  gap: 10px;
  color: var(--bg-gcs-muted);
  font-size: 13px;
  font-weight: 700;
}

.bg-gcs-practice-question {
  font-size: 16px;
  font-weight: 800;
  margin-bottom: 14px;
}

.bg-gcs-choices {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
  gap: 10px;
}

.bg-gcs-choice,
.bg-gcs-reveal-toggle {
  border: 1px solid rgba(15, 23, 42, 0.14);
  border-radius: 12px;
  background: #fff;
  padding: 10px 14px;
  cursor: pointer;
  font: inherit;
  font-weight: 750;
  transition: transform .15s ease, border-color .15s ease, background .15s ease;
}

.bg-gcs-choice:hover,
.bg-gcs-reveal-toggle:hover {
  transform: translateY(-1px);
  border-color: var(--bg-gcs-accent);
}

.bg-gcs-choice.is-correct {
  border-color: rgba(34,197,94,0.45);
  background: rgba(34,197,94,0.10);
  color: #166534;
}

.bg-gcs-choice.is-wrong {
  border-color: rgba(239,68,68,0.42);
  background: rgba(239,68,68,0.08);
  color: #991b1b;
}

.bg-gcs-practice-feedback,
.bg-gcs-explanation,
.bg-gcs-reveal-content {
  margin-top: 14px;
  padding: 13px 14px;
  border-radius: 14px;
  background: rgba(10,102,194,0.08);
  border: 1px solid rgba(10,102,194,0.16);
}

.bg-gcs-practice-feedback.is-correct {
  background: rgba(34,197,94,0.10);
  border-color: rgba(34,197,94,0.22);
  color: #166534;
}

.bg-gcs-practice-feedback.is-wrong {
  background: rgba(239,68,68,0.08);
  border-color: rgba(239,68,68,0.20);
  color: #991b1b;
}

.bg-gcs-summary-list {
  margin: 0;
  padding-left: 20px;
}

.bg-gcs-summary-list li {
  margin: 8px 0;
}

.bg-gcs-reveal-toggle {
  background: var(--bg-gcs-accent);
  color: #fff;
  border-color: var(--bg-gcs-accent);
}

@media (max-width: 720px) {
  .bg-gcs-rule,
  .bg-gcs-formula,
  .bg-gcs-correct-wrong,
  .bg-gcs-mistake,
  .bg-gcs-compare,
  .bg-gcs-timeline,
  .bg-gcs-practice,
  .bg-gcs-reveal,
  .bg-gcs-summary,
  .bg-gcs-pattern {
    padding: 15px;
    border-radius: 16px;
  }

  .bg-gcs-correct-wrong,
  .bg-gcs-mini-grid {
    grid-template-columns: 1fr;
  }

  .bg-gcs-table thead {
    display: none;
  }

  .bg-gcs-table,
  .bg-gcs-table tbody,
  .bg-gcs-table tr,
  .bg-gcs-table td {
    display: block;
    width: 100%;
  }

  .bg-gcs-table tr {
    border-bottom: 1px solid rgba(15, 23, 42, 0.10);
    padding: 10px 0;
  }

  .bg-gcs-table td {
    border: 0;
    padding: 7px 12px;
  }

  .bg-gcs-table td::before {
    content: attr(data-label);
    display: block;
    color: var(--bg-gcs-muted);
    font-size: 12px;
    font-weight: 800;
    margin-bottom: 3px;
    text-transform: uppercase;
    letter-spacing: .03em;
  }
}

/* v1.2 Example Sentence Box */
.bg-gcs-example {
  position: relative;
  border-left: 5px solid var(--bg-gcs-accent);
}

.bg-gcs-example-sentence {
  font-size: 18px;
  line-height: 1.65;
  font-weight: 700;
  color: var(--bg-gcs-text);
}

.bg-gcs-example-sentence p {
  margin: 0;
}

.bg-gcs-example-translation {
  margin-top: 12px;
  padding: 10px 12px;
  border-radius: 12px;
  background: rgba(10, 102, 194, 0.08);
  color: var(--bg-gcs-muted);
  font-size: 14px;
}

.bg-gcs-example-translation span {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  margin-right: 8px;
  width: 28px;
  height: 22px;
  border-radius: 999px;
  background: var(--bg-gcs-accent);
  color: #fff;
  font-size: 11px;
  font-weight: 800;
}