:root {
  --java-ink: #1f2937;
  --java-muted: #5f6b7a;
  --java-panel: #ffffff;
  --java-soft: #f7f4ed;
  --java-accent: #e07a5f;
  --java-blue: #2563eb;
  --java-green: #15803d;
  --java-border: #1f2937;
}

body {
  font-family: var(--nb-font-primary, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif);
  background: var(--nb-bg-light, var(--java-soft));
  color: var(--nb-text-primary, var(--java-ink));
}

.en-content,
.zh-content {
  transition: opacity .15s ease;
}

html.lang-zh .en-content,
body.lang-zh .en-content {
  display: none !important;
}

html.lang-zh .zh-content,
body.lang-zh .zh-content {
  display: inline !important;
}

html:not(.lang-zh) .en-content,
body:not(.lang-zh) .en-content {
  display: inline !important;
}

html:not(.lang-zh) .zh-content,
body:not(.lang-zh) .zh-content {
  display: none !important;
}

.knowledge-shell {
  max-width: 1120px;
  margin: 0 auto;
  padding: 2rem 1rem 4rem;
}

.knowledge-back {
  display: inline-flex;
  align-items: center;
  gap: .5rem;
  margin-bottom: 1.5rem;
  padding: .75rem 1rem;
  background: var(--java-panel);
  border: 2px solid var(--java-border);
  color: inherit;
  text-decoration: none;
  font-weight: 800;
  box-shadow: 3px 3px 0 var(--java-border);
}

.knowledge-back:hover {
  transform: translate(2px, 2px);
  box-shadow: 1px 1px 0 var(--java-border);
}

.knowledge-hero {
  border: 3px solid var(--java-border);
  background: #fff7ed;
  padding: clamp(1.5rem, 4vw, 3rem);
  box-shadow: 8px 8px 0 var(--java-border);
  margin-bottom: 2rem;
}

.knowledge-label {
  display: inline-block;
  border: 2px solid var(--java-border);
  background: #d9f99d;
  padding: .35rem .65rem;
  font-weight: 900;
  text-transform: uppercase;
  font-size: .8rem;
  margin-bottom: .9rem;
}

.knowledge-title {
  font-size: clamp(2.2rem, 6vw, 4.5rem);
  line-height: 1;
  margin: 0 0 1rem;
  font-weight: 950;
  letter-spacing: 0;
}

.knowledge-subtitle {
  max-width: 760px;
  color: var(--java-muted);
  font-size: 1.1rem;
  line-height: 1.7;
  margin: 0;
}

.knowledge-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 1.25rem;
  margin: 1.5rem 0 2rem;
}

.knowledge-grid.two {
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
}

.knowledge-card,
.concept-block,
.code-block,
.term-table {
  background: var(--java-panel);
  border: 2px solid var(--java-border);
  box-shadow: 5px 5px 0 var(--java-border);
}

.knowledge-card {
  display: flex;
  flex-direction: column;
  min-height: 220px;
  padding: 1.25rem;
  color: inherit;
  text-decoration: none;
  transition: transform .15s ease, box-shadow .15s ease;
}

.knowledge-card:hover {
  transform: translate(-3px, -3px);
  box-shadow: 8px 8px 0 var(--java-border);
}

.knowledge-card.primary {
  min-height: 300px;
  background: #eff6ff;
}

.knowledge-card.secondary {
  background: #f0fdf4;
}

.knowledge-card h2,
.knowledge-card h3 {
  margin: 0 0 .7rem;
  font-size: 1.5rem;
  font-weight: 950;
}

.knowledge-card p,
.concept-block p,
.term-table p {
  color: var(--java-muted);
  line-height: 1.65;
}

.knowledge-tags {
  display: flex;
  flex-wrap: wrap;
  gap: .5rem;
  margin-top: auto;
}

.knowledge-tag {
  display: inline-flex;
  border: 2px solid var(--java-border);
  background: #fef08a;
  padding: .25rem .5rem;
  font-size: .75rem;
  font-weight: 900;
}

.section-heading {
  margin: 2.5rem 0 1rem;
  font-size: clamp(1.5rem, 3vw, 2.2rem);
  font-weight: 950;
}

.concept-block {
  padding: 1.25rem;
  margin: 1rem 0;
}

.concept-block h2,
.concept-block h3 {
  margin: 0 0 .65rem;
  font-weight: 950;
}

.concept-block ul {
  margin: .75rem 0 0 1.15rem;
  color: var(--java-muted);
  line-height: 1.7;
}

.concept-block li + li {
  margin-top: .35rem;
}

.concept-name {
  display: inline-block;
  padding: .25rem .5rem;
  border: 2px solid var(--java-border);
  background: #bfdbfe;
  font-weight: 900;
  margin-bottom: .65rem;
}

.simple-diagram {
  display: grid;
  gap: .75rem;
  margin: 1rem 0;
}

.diagram-row {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: .55rem;
}

.diagram-box {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  padding: .5rem .8rem;
  border: 2px solid var(--java-border);
  background: #fff;
  font-weight: 900;
}

.diagram-arrow {
  font-weight: 950;
}

.code-block {
  padding: 1rem;
  margin: 1rem 0;
  overflow-x: auto;
  background: #111827;
  color: #f9fafb;
}

.code-block code {
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", monospace;
  font-size: .92rem;
  line-height: 1.65;
  white-space: pre;
}

.term-table {
  width: 100%;
  border-collapse: collapse;
  margin: 1rem 0 2rem;
}

.term-table th,
.term-table td {
  border: 2px solid var(--java-border);
  padding: .85rem;
  text-align: left;
  vertical-align: top;
}

.term-table th {
  background: #fde68a;
  font-weight: 950;
}

.term-table td {
  background: #fff;
  color: var(--java-muted);
}

.callout {
  border: 2px solid var(--java-border);
  background: #ecfccb;
  padding: 1rem;
  margin: 1rem 0;
  font-weight: 800;
  line-height: 1.6;
}

.page-nav {
  display: flex;
  flex-wrap: wrap;
  gap: .75rem;
  margin: 1.5rem 0 2rem;
}

.page-nav a {
  border: 2px solid var(--java-border);
  background: #fff;
  color: inherit;
  padding: .6rem .8rem;
  text-decoration: none;
  font-weight: 850;
}

.quiz-status {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: .75rem;
  margin: 1rem 0 1.5rem;
  padding: 1rem;
  border: 2px solid var(--java-border);
  background: #fff;
  box-shadow: 4px 4px 0 var(--java-border);
  position: sticky;
  top: .75rem;
  z-index: 5;
}

.quiz-progress {
  flex: 1 1 220px;
  height: 16px;
  border: 2px solid var(--java-border);
  background: #f3f4f6;
  overflow: hidden;
}

.quiz-progress-fill {
  width: 0;
  height: 100%;
  background: var(--java-accent);
  transition: width .2s ease;
}

.quiz-score {
  font-weight: 950;
}

.question-card {
  background: #fff;
  border: 2px solid var(--java-border);
  box-shadow: 4px 4px 0 var(--java-border);
  margin: 1rem 0;
  padding: 1rem;
}

.question-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: .5rem;
  margin-bottom: .75rem;
}

.question-number,
.difficulty-pill {
  border: 2px solid var(--java-border);
  padding: .2rem .5rem;
  font-weight: 950;
  font-size: .78rem;
}

.question-number {
  background: #bfdbfe;
}

.difficulty-pill.basic {
  background: #bbf7d0;
}

.difficulty-pill.intermediate {
  background: #fde68a;
}

.difficulty-pill.advanced {
  background: #fecaca;
}

.question-text {
  font-weight: 900;
  line-height: 1.55;
  margin: .5rem 0 1rem;
}

.option-list {
  display: grid;
  gap: .55rem;
}

.option-button {
  width: 100%;
  text-align: left;
  border: 2px solid var(--java-border);
  background: #fff;
  padding: .75rem;
  cursor: pointer;
  font-weight: 750;
  line-height: 1.45;
}

.option-button:hover {
  background: #eff6ff;
}

.option-button.selected {
  background: #fef08a;
}

.option-button.correct {
  background: #bbf7d0;
}

.option-button.incorrect {
  background: #fecaca;
}

.explanation {
  display: none;
  margin-top: .8rem;
  padding: .8rem;
  border: 2px dashed var(--java-border);
  background: #f0f9ff;
  color: var(--java-muted);
  line-height: 1.6;
}

.quiz-actions {
  display: flex;
  flex-wrap: wrap;
  gap: .75rem;
  margin: 1.5rem 0;
}

.quiz-button {
  border: 2px solid var(--java-border);
  background: var(--java-accent);
  color: #fff;
  padding: .8rem 1rem;
  font-weight: 950;
  cursor: pointer;
  box-shadow: 3px 3px 0 var(--java-border);
}

.quiz-button.secondary {
  background: #fff;
  color: var(--java-ink);
}

.quiz-button:hover {
  transform: translate(2px, 2px);
  box-shadow: 1px 1px 0 var(--java-border);
}

.result-panel {
  display: none;
  border: 3px solid var(--java-border);
  background: #ecfccb;
  box-shadow: 6px 6px 0 var(--java-border);
  padding: 1.25rem;
  margin: 1rem 0 2rem;
}

[data-theme="dark"] .knowledge-hero,
html.dark .knowledge-hero,
[data-theme="dark"] .knowledge-card,
html.dark .knowledge-card,
[data-theme="dark"] .concept-block,
html.dark .concept-block,
[data-theme="dark"] .term-table,
html.dark .term-table,
[data-theme="dark"] .term-table td,
html.dark .term-table td {
  background: #242424 !important;
  color: #ffffff !important;
  border-color: #ffffff !important;
  box-shadow: 5px 5px 0 #ffffff !important;
}

[data-theme="dark"] .knowledge-subtitle,
[data-theme="dark"] .knowledge-card p,
[data-theme="dark"] .concept-block p,
[data-theme="dark"] .concept-block li,
html.dark .knowledge-subtitle,
html.dark .knowledge-card p,
html.dark .concept-block p,
html.dark .concept-block li {
  color: #d1d5db !important;
}

@media (max-width: 640px) {
  .knowledge-shell {
    padding: 1rem .75rem 3rem;
  }

  .knowledge-card.primary {
    min-height: 240px;
  }

  .term-table,
  .term-table tbody,
  .term-table tr,
  .term-table th,
  .term-table td {
    display: block;
  }
}