:root {
  --navy: #123152;
  --navy-dark: #0a2238;
  --navy-deep: #081c2e;
  --accent: #1f6feb;
  --accent-dark: #174ea6;
  --accent-soft: #e7f0fb;
  --text: #26313f;
  --muted: #5a6b7c;
  --faint: #8fa1b3;
  --bg: #f4f6fa;
  --card: #ffffff;
  --line: #e3e8f0;
  --good: #0e7a50;
  --good-bg: #e9f7f0;
  --bad: #b3273a;
  --bad-bg: #fceef0;
  --warn-bg: #fdf6e6;
  --warn: #8a6414;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: -apple-system, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

a {
  color: var(--accent-dark);
}

.skip {
  position: absolute;
  left: -999px;
}

.skip:focus {
  left: 1rem;
  top: 1rem;
  z-index: 50;
  background: #fff;
  padding: 0.5rem 1rem;
  border-radius: 6px;
}

.nav {
  background: var(--navy);
  color: #fff;
  position: sticky;
  top: 0;
  z-index: 20;
  box-shadow: 0 2px 8px rgba(4, 20, 36, 0.25);
}

.nav-inner {
  max-width: 1120px;
  margin: 0 auto;
  padding: 0.85rem 1.5rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
}

.nav .logo {
  font-weight: 800;
  font-size: 1.3rem;
  letter-spacing: 0.04em;
  color: #fff;
  text-decoration: none;
  display: flex;
  align-items: center;
  gap: 0.55rem;
}

.nav .logo svg {
  flex: 0 0 auto;
}

.nav ul {
  list-style: none;
  display: flex;
  gap: 0.25rem;
  flex-wrap: wrap;
}

.nav ul li a {
  color: #cfe0f3;
  text-decoration: none;
  font-size: 0.92rem;
  font-weight: 500;
  padding: 0.45rem 0.8rem;
  border-radius: 6px;
  transition: background 0.15s, color 0.15s;
}

.nav ul li a:hover,
.nav ul li a.current {
  background: rgba(255, 255, 255, 0.14);
  color: #fff;
}

.page-head {
  background: linear-gradient(135deg, var(--navy), var(--navy-dark));
  color: #fff;
  padding: 3.2rem 1.5rem 3rem;
  text-align: center;
}

.page-head h1 {
  font-size: 2.3rem;
  font-weight: 700;
  letter-spacing: 0.01em;
  max-width: 860px;
  margin: 0 auto 0.55rem;
}

.page-head p {
  color: #bed0e4;
  font-size: 1.08rem;
  max-width: 720px;
  margin: 0 auto;
}

.page-head .crumbs {
  color: #94abca;
  font-size: 0.85rem;
  margin-top: 1rem;
}

.page-head .crumbs a {
  color: #cdddf0;
  text-decoration: none;
}

.crumb-sep {
  margin: 0 0.4rem;
  color: #7e95b6;
}

main {
  flex: 1;
  padding: 2.6rem 1.5rem;
}

main > .wrap,
.wrap {
  max-width: 1120px;
  margin: 0 auto;
}

.section {
  margin-bottom: 2.6rem;
}

.section h2 {
  color: var(--navy);
  font-size: 1.5rem;
  margin-bottom: 0.35rem;
}

.section .lede {
  color: var(--muted);
  max-width: 760px;
  margin-bottom: 1.4rem;
}

.section h3 {
  color: var(--navy);
  font-size: 1.15rem;
  margin: 1.2rem 0 0.4rem;
}

.section h4 {
  color: var(--accent-dark);
  margin: 1rem 0 0.3rem;
}

.section p {
  color: var(--muted);
  font-size: 1rem;
  margin: 0.55rem 0;
}

.section p b,
.section li b {
  color: var(--text);
}

.hero {
  background: var(--card);
  border-radius: 14px;
  padding: 2.6rem;
  box-shadow: 0 1px 4px rgba(9, 33, 58, 0.08);
  border: 1px solid var(--line);
}

.hero .content h2 {
  font-size: 1.65rem;
}

.hero .content p {
  max-width: 640px;
  margin: 0.75rem 0 1.25rem;
}

.btn {
  display: inline-block;
  background: var(--accent);
  color: #fff;
  padding: 0.7rem 1.4rem;
  border-radius: 8px;
  text-decoration: none;
  font-weight: 600;
  font-size: 0.95rem;
  border: 1px solid transparent;
  cursor: pointer;
  transition: background 0.15s;
}

.btn:hover {
  background: var(--accent-dark);
}

.btn.ghost {
  background: transparent;
  color: var(--accent-dark);
  border-color: var(--accent);
}

.btn.ghost:hover {
  background: var(--accent-soft);
}

.btn.small {
  padding: 0.45rem 0.9rem;
  font-size: 0.85rem;
}

.grid {
  display: grid;
  gap: 1.3rem;
}

.grid.cols-2 {
  grid-template-columns: 1fr 1fr;
}

.grid.cols-3 {
  grid-template-columns: repeat(3, 1fr);
}

.grid.cols-4 {
  grid-template-columns: repeat(4, 1fr);
}

.grid.cols-raw {
  grid-template-columns: 260px 1fr;
}

.card {
  background: var(--card);
  border-radius: 12px;
  padding: 1.4rem;
  border: 1px solid var(--line);
  box-shadow: 0 1px 3px rgba(9, 33, 58, 0.06);
}

.card h3 {
  font-size: 1.08rem;
  margin-bottom: 0.35rem;
}

.card p {
  font-size: 0.94rem;
  margin: 0.35rem 0;
}

.card .tagline {
  color: var(--accent-dark);
  font-weight: 600;
  font-size: 0.8rem;
  letter-spacing: 0.05em;
  margin-bottom: 0.5rem;
}

.card .meta {
  color: var(--faint);
  font-size: 0.8rem;
  margin-top: 0.6rem;
}

.card .meta .date {
  margin-right: 0.8rem;
}

.course-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
  gap: 1.3rem;
}

.course-card {
  background: var(--card);
  border-radius: 12px;
  padding: 1.4rem;
  border: 1px solid var(--line);
  box-shadow: 0 1px 3px rgba(9, 33, 58, 0.06);
  display: flex;
  flex-direction: column;
}

.course-card .level {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  color: var(--accent-dark);
  background: var(--accent-soft);
  padding: 0.18rem 0.6rem;
  border-radius: 999px;
  align-self: flex-start;
  margin-bottom: 0.7rem;
}

.course-card h3 {
  margin-bottom: 0.35rem;
}

.course-card p {
  flex: 1;
  font-size: 0.92rem;
}

.course-card .foot {
  margin-top: 0.9rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--faint);
  font-size: 0.8rem;
}

.topic-grid,
.author-grid,
.term-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 1rem;
}

.topic-grid div,
.author-grid div,
.term-grid div {
  background: var(--card);
  padding: 1.3rem;
  text-align: center;
  border-radius: 10px;
  border: 1px solid var(--line);
  box-shadow: 0 1px 3px rgba(9, 33, 58, 0.05);
  font-weight: 600;
  color: var(--navy);
}

.timeline {
  background: var(--card);
  border-radius: 12px;
  padding: 1.6rem 1.8rem;
  border-left: 4px solid var(--accent);
  box-shadow: 0 1px 4px rgba(9, 33, 58, 0.06);
}

.period {
  margin-bottom: 1.6rem;
}

.period h3 {
  color: var(--accent-dark);
  border-bottom: 1px solid var(--line);
  padding-bottom: 0.45rem;
  margin-bottom: 0.6rem;
}

.period ul {
  list-style: none;
}

.period ul li {
  padding: 0.28rem 0;
  color: var(--muted);
}

.period ul li::before {
  content: '';
  display: inline-block;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--accent);
  margin-right: 0.6rem;
}

.accordion details {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 10px;
  margin-bottom: 0.8rem;
  padding: 1rem 1.3rem;
}

.accordion summary {
  cursor: pointer;
  font-weight: 600;
  color: var(--navy);
  font-size: 1rem;
}

.accordion details p {
  margin-top: 0.6rem;
  color: var(--muted);
}

.table-wrap {
  overflow-x: auto;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
}

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.94rem;
}

th,
td {
  text-align: left;
  padding: 0.7rem 1rem;
  border-bottom: 1px solid var(--line);
}

thead th {
  background: var(--navy);
  color: #fff;
  font-weight: 600;
  letter-spacing: 0.03em;
}

tbody tr:nth-child(even) {
  background: #fafbfe;
}

tbody tr:hover {
  background: var(--accent-soft);
}

.callout {
  border-radius: 10px;
  padding: 1rem 1.2rem;
  margin: 1.1rem 0;
  font-size: 0.95rem;
  border-left: 4px solid transparent;
}

.callout.note {
  background: var(--accent-soft);
  border-left-color: var(--accent);
}

.callout.warn {
  background: var(--warn-bg);
  border-left-color: var(--warn);
}

.callout.good {
  background: var(--good-bg);
  border-left-color: var(--good);
}

.callout p {
  margin: 0;
  color: var(--text);
}

.callout b {
  color: var(--navy);
}

.code {
  background: #0d1b2a;
  color: #d7e4f3;
  border-radius: 10px;
  padding: 1.1rem 1.3rem;
  overflow-x: auto;
  font-family: 'SF Mono', Menlo, Consolas, monospace;
  font-size: 0.88rem;
  line-height: 1.6;
  margin: 0.9rem 0;
}

.code .cmt {
  color: #6b7f98;
}

.figure {
  margin: 1.1rem 0;
}

.figure figcaption {
  color: var(--faint);
  font-size: 0.82rem;
  margin-top: 0.4rem;
}

figure {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 1.2rem;
  text-align: center;
}

figure svg {
  max-width: 100%;
  height: auto;
}

blockquote {
  border-left: 3px solid var(--accent);
  background: var(--accent-soft);
  border-radius: 0 10px 10px 0;
  padding: 1rem 1.3rem;
  margin: 1.1rem 0;
  color: var(--text);
}

blockquote p {
  margin: 0;
  color: var(--text);
}

blockquote footer {
  color: var(--faint);
  font-size: 0.85rem;
  margin-top: 0.4rem;
}

.language-tags,
.chips {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
  margin-bottom: 1.2rem;
}

.language-tags span,
.chip {
  background: var(--accent-soft);
  color: var(--accent-dark);
  padding: 0.42rem 0.95rem;
  border-radius: 999px;
  font-size: 0.88rem;
  font-weight: 600;
  border: 1px solid #cfe0f3;
}

.chip.active {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

.browse h2 {
  margin-bottom: 1.2rem;
}

.statbar {
  display: flex;
  gap: 1.4rem;
  flex-wrap: wrap;
  justify-content: center;
  margin-top: 1.4rem;
}

.statbar .stat {
  min-width: 120px;
}

.statbar .number {
  font-size: 1.9rem;
  font-weight: 800;
  color: #fff;
}

.statbar .capt {
  font-size: 0.82rem;
  color: #b9cbe2;
}

.quiz {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 1.4rem;
  margin: 1.2rem 0;
}

.quiz .q {
  font-weight: 600;
  color: var(--navy);
  margin-bottom: 0.8rem;
}

.quiz .options {
  display: grid;
  gap: 0.5rem;
}

.quiz .option {
  text-align: left;
  background: #fafbfe;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 0.6rem 0.9rem;
  cursor: pointer;
  font-size: 0.94rem;
  color: var(--text);
  font-family: inherit;
  transition: background 0.15s, border-color 0.15s;
}

.quiz .option:hover {
  border-color: var(--accent);
}

.quiz .option.correct {
  background: var(--good-bg);
  border-color: var(--good);
  color: var(--good);
  font-weight: 600;
}

.quiz .option.wrong {
  background: var(--bad-bg);
  border-color: var(--bad);
  color: var(--bad);
}

.quiz .feedback {
  margin-top: 0.7rem;
  font-size: 0.94rem;
  min-height: 1.5em;
}

.quiz .feedback.ok {
  color: var(--good);
}

.quiz .feedback.no {
  color: var(--bad);
}

.searchbox {
  position: relative;
  margin-bottom: 1.2rem;
}

.searchbox input {
  width: 100%;
  padding: 0.75rem 1rem 0.75rem 2.6rem;
  border: 1px solid var(--line);
  border-radius: 10px;
  font-size: 0.95rem;
  background: var(--card);
  outline: none;
}

.searchbox input:focus {
  border-color: var(--accent);
}

.searchbox svg {
  position: absolute;
  left: 0.8rem;
  top: 50%;
  transform: translateY(-50%);
  color: var(--faint);
}

.contact-form label {
  display: block;
  font-weight: 600;
  color: var(--navy);
  font-size: 0.92rem;
  margin: 0.9rem 0 0.3rem;
}

.contact-form input,
.contact-form textarea,
.contact-form select {
  width: 100%;
  padding: 0.7rem 0.9rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  font-size: 0.95rem;
  font-family: inherit;
  background: var(--card);
  outline: none;
}

.contact-form input:focus,
.contact-form textarea:focus,
.contact-form select:focus {
  border-color: var(--accent);
}

.contact-form textarea {
  min-height: 120px;
  resize: vertical;
}

.contact-form .form-msg {
  margin-top: 0.9rem;
  font-weight: 600;
}

.contact-form .form-msg.ok {
  color: var(--good);
}

.toc {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 1.2rem 1.4rem;
  font-size: 0.92rem;
}

.toc h3 {
  font-size: 0.95rem;
  margin-bottom: 0.6rem;
  letter-spacing: 0.05em;
}

.toc ol {
  padding-left: 1.2rem;
}

.toc li {
  margin: 0.35rem 0;
}

.pagination {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin: 1.6rem 0;
}

.kvtable td:first-child {
  font-weight: 600;
  color: var(--navy);
  width: 220px;
  background: #fafbfe;
}

.quicklinks {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 1rem;
  margin: 1.2rem 0;
}

.quicklinks a {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 1rem;
  text-decoration: none;
  color: var(--accent-dark);
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 0.6rem;
  transition: border-color 0.15s, background 0.15s;
}

.quicklinks a:hover {
  border-color: var(--accent);
  background: var(--accent-soft);
}

.progress-track {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 1.3rem;
}

.progress-track .bar {
  background: #e6ecf4;
  border-radius: 999px;
  height: 12px;
  overflow: hidden;
  margin-top: 0.6rem;
}

.progress-track .bar i {
  display: block;
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--accent-dark));
  border-radius: 999px;
  width: 0;
  transition: width 0.3s;
}

footer {
  background: var(--navy-deep);
  color: #9fb4cd;
  padding: 2.6rem 1.5rem 1.2rem;
}

footer .foot-grid {
  max-width: 1120px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: 2fr 1fr 1fr;
  gap: 2rem;
}

footer h4 {
  color: #fff;
  font-size: 0.95rem;
  margin-bottom: 0.8rem;
}

footer p {
  color: #9fb4cd;
  font-size: 0.9rem;
}

footer ul {
  list-style: none;
}

footer ul li {
  margin: 0.35rem 0;
}

footer ul li a {
  color: #b9cbe2;
  text-decoration: none;
  font-size: 0.9rem;
}

footer ul li a:hover {
  color: #fff;
  text-decoration: underline;
}

.hero-svg {
  max-width: 100%;
  height: auto;
  display: block;
}

.hero-visual {
  background: linear-gradient(135deg, var(--navy) 0%, var(--navy-dark) 100%);
  border-radius: 18px;
  padding: 1.2rem 1.4rem;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 1.1rem 0 0;
}

.pic {
  border-radius: 14px;
  border: 1px solid var(--line);
  background: var(--accent-soft);
  padding: 1rem;
  display: flex;
  justify-content: center;
  align-items: center;
  margin: 1rem 0;
}

.pic svg {
  width: 100%;
  height: auto;
  max-width: 560px;
}

.stat-num {
  font-size: 2rem;
  font-weight: 800;
  color: var(--accent);
}

.actionbox {
  background: var(--navy);
  color: #dbe7f5;
  border-radius: 16px;
  padding: 1.4rem;
  margin: 1.4rem 0;
}

.actionbox h3 {
  color: #fff;
  margin-top: 0;
}

.actionbox .btn {
  margin-top: 0.8rem;
}

.flashcard {
  perspective: 1200px;
  cursor: pointer;
}

.flashcard-inner {
  position: relative;
  transition: transform 0.5s;
  transform-style: preserve-3d;
  min-height: 180px;
}

.flashcard.flip .flashcard-inner {
  transform: rotateY(180deg);
}

.flashcard-face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  border-radius: 14px;
  padding: 1.1rem 1.2rem;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.flashcard-front {
  background: var(--card);
  border: 1px solid var(--line);
}

.flashcard-back {
  background: var(--navy);
  color: #dbe7f5;
  transform: rotateY(180deg);
}

.flashcard-back h4 {
  color: #fff;
  margin-top: 0;
}

.cookiebar {
  position: fixed;
  left: 50%;
  bottom: 1rem;
  transform: translateX(-50%) translateY(140%);
  width: min(94vw, 640px);
  background: var(--navy-deep);
  color: #c9d8e8;
  border: 1px solid rgba(255, 255, 255, 0.14);
  border-radius: 16px;
  padding: 1.1rem 1.2rem;
  box-shadow: 0 14px 40px rgba(8, 28, 46, 0.45);
  z-index: 900;
  transition: transform 0.45s ease;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.8rem;
}

.cookiebar.show {
  transform: translateX(-50%) translateY(0);
}

.cookiebar p {
  flex: 1 1 300px;
  margin: 0;
  font-size: 0.9rem;
}

.cookiebar a {
  color: #fff;
}

.cookiebar .rowbtns {
  display: flex;
  gap: 0.5rem;
}

.toast {
  position: fixed;
  right: 1.2rem;
  bottom: 1.2rem;
  background: var(--navy-deep);
  color: #eef4fb;
  border: 1px solid rgba(255, 255, 255, 0.14);
  border-radius: 12px;
  padding: 0.85rem 1.1rem;
  font-size: 0.9rem;
  box-shadow: 0 12px 32px rgba(8, 28, 46, 0.4);
  z-index: 950;
  opacity: 0;
  transform: translateY(10px);
  pointer-events: none;
  transition: opacity 0.3s ease, transform 0.3s ease;
}

.toast.show {
  opacity: 1;
  transform: translateY(0);
  pointer-events: auto;
}

details.faq-item {
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--card);
  margin: 0.6rem 0;
  overflow: hidden;
}

details.faq-item summary {
  list-style: none;
  cursor: pointer;
  padding: 0.95rem 1.05rem;
  font-weight: 700;
  color: var(--navy);
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
}

details.faq-item summary::-webkit-details-marker {
  display: none;
}

details.faq-item summary::after {
  content: "+";
  font-size: 1.3rem;
  color: var(--accent);
  transition: transform 0.2s;
}

details.faq-item[open] summary::after {
  transform: rotate(45deg);
}

details.faq-item .faq-a {
  padding: 0 1.05rem 1rem;
  color: var(--muted);
  font-size: 0.94rem;
}

.cookie-link {
  font-size: 0.8rem;
  cursor: pointer;
  color: var(--faint);
  background: none;
  border: none;
  padding: 0;
  text-decoration: underline;
}

.print-tip {
  display: none;
}

footer .bottom {
  max-width: 1120px;
  margin: 2rem auto 0;
  padding-top: 1.2rem;
  border-top: 1px solid rgba(255, 255, 255, 0.12);
  text-align: center;
  font-size: 0.82rem;
  color: #7e95b6;
}

footer .bottom a {
  color: #b9cbe2;
}

@media (max-width: 860px) {
  .nav-inner {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.5rem;
  }
  .nav ul {
    gap: 0.15rem;
  }
  .grid.cols-2,
  .grid.cols-3,
  .grid.cols-4,
  .grid.cols-raw {
    grid-template-columns: 1fr;
  }
  footer .foot-grid {
    grid-template-columns: 1fr 1fr;
  }
  .page-head h1 {
    font-size: 1.8rem;
  }
  .hero {
    padding: 1.6rem;
  }
  .section {
    margin-bottom: 2rem;
  }
}

@media print {
  .nav,
  footer,
  .btn,
  .quiz .option,
  .cookiebar,
  .toast {
    display: none;
  }
  .print-tip {
    display: block;
  }
  body {
    background: #fff;
  }
  .hero,
  .card,
  .timeline {
    box-shadow: none;
    border: 1px solid #ccc;
  }
}