:root {
  color-scheme: light;
  --ink: #071126;
  --muted: #536078;
  --paper: #f7f9ff;
  --surface: #ffffff;
  --line: #dce5f3;
  --blue: #0c4fb3;
  --blue-dark: #08235f;
  --green: #0d7a4f;
  --gold: #ffd21c;
  --red: #e22d2d;
  --purple: #7b3f98;
  --shadow: 0 18px 50px rgba(7, 17, 38, 0.12);
  --radius: 8px;
  --max: 1180px;
}

@media (max-width: 640px) {
  .source-links {
    grid-template-columns: 1fr;
  }
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: "Segoe UI", Arial, sans-serif;
  line-height: 1.55;
}

body.auth-pending {
  overflow: hidden;
}

body.auth-pending .site-shell {
  filter: blur(8px);
  pointer-events: none;
  user-select: none;
}

img {
  max-width: 100%;
  display: block;
}

a {
  color: inherit;
}

.site-shell {
  min-height: 100vh;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  background: rgba(255, 255, 255, 0.94);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(14px);
}

.topbar-inner {
  width: min(var(--max), calc(100% - 32px));
  margin: 0 auto;
  min-height: 76px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
}

.brand-lockup {
  display: flex;
  align-items: center;
  gap: 12px;
  min-width: 0;
  text-decoration: none;
}

.brand-lockup img {
  width: 52px;
  height: 52px;
  object-fit: cover;
  border-radius: 8px;
  border: 1px solid #cbd7eb;
}

.brand-text {
  min-width: 0;
}

.brand-text strong,
.brand-text span {
  display: block;
}

.brand-text strong {
  font-size: 1.02rem;
  line-height: 1.1;
}

.brand-text span {
  color: var(--muted);
  font-size: 0.84rem;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.nav {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.session-actions {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.session-actions button {
  border: 1px solid var(--line);
  background: #fff;
  color: var(--blue-dark);
  border-radius: var(--radius);
  padding: 8px 11px;
  font: inherit;
  font-weight: 900;
  cursor: pointer;
}

.session-actions [data-logout] {
  background: #fff3f3;
  color: #9f1d1d;
}

.auth-gate {
  position: fixed;
  inset: 0;
  z-index: 100;
  display: grid;
  place-items: center;
  padding: 18px;
  background:
    linear-gradient(135deg, rgba(7, 17, 38, 0.82), rgba(12, 79, 179, 0.78)),
    url("assets/solarpv.png") center / cover no-repeat;
}

.auth-card {
  width: min(520px, 100%);
  max-height: min(720px, calc(100vh - 30px));
  overflow: auto;
  background: rgba(255, 255, 255, 0.97);
  border: 1px solid rgba(255, 255, 255, 0.75);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 20px;
}

.auth-brand {
  display: grid;
  grid-template-columns: 62px minmax(0, 1fr);
  gap: 12px;
  align-items: center;
  margin-bottom: 16px;
}

.auth-brand img {
  width: 62px;
  height: 62px;
  object-fit: cover;
  border-radius: var(--radius);
  border: 1px solid var(--line);
}

.auth-brand strong,
.auth-brand span {
  display: block;
}

.auth-brand strong {
  color: var(--blue-dark);
  font-size: 1.12rem;
  line-height: 1.14;
}

.auth-brand span {
  color: var(--muted);
  font-size: 0.9rem;
}

.auth-tabs {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
  margin-bottom: 14px;
}

.auth-tabs button {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #f7f9ff;
  color: var(--blue-dark);
  padding: 10px;
  font: inherit;
  font-weight: 900;
  cursor: pointer;
}

.auth-tabs button.active {
  background: var(--blue);
  color: #fff;
  border-color: var(--blue);
}

.auth-form {
  display: grid;
  gap: 11px;
}

.auth-form.compact {
  margin-top: 16px;
}

.auth-form label {
  display: grid;
  gap: 5px;
  color: #1f2c47;
  font-weight: 800;
}

.auth-form input {
  width: 100%;
  border: 1px solid #c9d5e8;
  border-radius: var(--radius);
  padding: 11px 12px;
  font: inherit;
  background: #fff;
}

.auth-form button,
.admin-sheet-link {
  display: inline-flex;
  justify-content: center;
  align-items: center;
  min-height: 42px;
  border: 0;
  border-radius: var(--radius);
  background: var(--green);
  color: #fff;
  padding: 10px 14px;
  font: inherit;
  font-weight: 900;
  text-decoration: none;
  cursor: pointer;
}

.auth-status {
  min-height: 22px;
  margin: 12px 0 0;
  color: var(--green);
  font-weight: 800;
}

.auth-status.error {
  color: #b92323;
}

.auth-meta {
  display: grid;
  gap: 4px;
  margin-top: 12px;
  color: var(--muted);
  font-size: 0.82rem;
}

.admin-drawer {
  position: fixed;
  top: 88px;
  right: 18px;
  z-index: 90;
  width: min(390px, calc(100vw - 28px));
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 18px;
}

.admin-drawer-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 10px;
}

.admin-drawer-head strong {
  color: var(--blue-dark);
  font-size: 1.12rem;
}

.admin-drawer-head button {
  border: 1px solid var(--line);
  background: #fff;
  border-radius: var(--radius);
  padding: 7px 10px;
  font: inherit;
  font-weight: 900;
  cursor: pointer;
}

.admin-drawer p {
  margin: 0 0 12px;
  color: var(--muted);
}

.admin-device {
  display: grid;
  gap: 5px;
  margin-top: 14px;
  color: var(--muted);
}

.admin-device code {
  overflow-wrap: anywhere;
  background: #eef4ff;
  color: var(--blue-dark);
  border-radius: var(--radius);
  padding: 8px;
}

.nav a,
.mini-button,
.test-jump a {
  text-decoration: none;
  border: 1px solid var(--line);
  background: #fff;
  border-radius: var(--radius);
  padding: 8px 12px;
  font-weight: 700;
  color: #1f2c47;
  transition: transform 160ms ease, border-color 160ms ease, background 160ms ease;
}

.nav a:hover,
.mini-button:hover,
.test-jump a:hover {
  transform: translateY(-1px);
  border-color: #aab9d3;
  background: #eef4ff;
}

.hero {
  background:
    linear-gradient(135deg, rgba(8, 35, 95, 0.95), rgba(12, 79, 179, 0.88)),
    radial-gradient(circle at 80% 20%, rgba(255, 210, 28, 0.26), transparent 34%),
    linear-gradient(135deg, #07183f, #0d7a4f);
  color: #fff;
}

.hero-inner {
  width: min(var(--max), calc(100% - 32px));
  margin: 0 auto;
  padding: 54px 0 40px;
  display: grid;
  grid-template-columns: minmax(0, 1.08fr) minmax(300px, 0.72fr);
  gap: 34px;
  align-items: center;
}

.eyebrow {
  display: inline-flex;
  gap: 8px;
  align-items: center;
  color: #08235f;
  background: var(--gold);
  border-radius: var(--radius);
  padding: 7px 10px;
  font-weight: 900;
  text-transform: uppercase;
  font-size: 0.78rem;
}

.hero h1 {
  margin: 18px 0 14px;
  font-size: clamp(2.15rem, 5vw, 4.9rem);
  line-height: 0.98;
  letter-spacing: 0;
}

.hero-copy {
  max-width: 760px;
  color: #e8eefc;
  font-size: 1.12rem;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 24px;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  padding: 10px 16px;
  border-radius: var(--radius);
  font-weight: 900;
  text-decoration: none;
  border: 2px solid transparent;
}

.button.primary {
  color: #08235f;
  background: var(--gold);
}

.button.secondary {
  color: #fff;
  border-color: rgba(255, 255, 255, 0.5);
}

.hero-card {
  background: rgba(255, 255, 255, 0.96);
  color: var(--ink);
  border-radius: var(--radius);
  padding: 12px;
  border: 1px solid rgba(255, 255, 255, 0.55);
  box-shadow: var(--shadow);
}

.hero-card img:first-child {
  width: 100%;
  border-radius: var(--radius);
  border: 1px solid var(--line);
  aspect-ratio: 633 / 420;
  object-fit: cover;
}

.credential-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
  margin-top: 14px;
}

.credential-grid strong,
.credential-grid span {
  display: block;
  text-align: center;
}

.credential-grid strong {
  color: var(--blue-dark);
  font-size: 1.45rem;
}

.credential-grid span {
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 700;
}

.section {
  width: min(var(--max), calc(100% - 32px));
  margin: 0 auto;
  padding: 48px 0;
}

.section-heading {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 20px;
  align-items: end;
  margin-bottom: 24px;
}

.section-heading h2 {
  margin: 0 0 6px;
  font-size: clamp(1.65rem, 3vw, 2.6rem);
  line-height: 1.08;
  color: var(--blue-dark);
}

.section-heading p {
  margin: 0;
  color: var(--muted);
  max-width: 760px;
}

.band {
  background: #fff;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}

.pill-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.pill {
  border-radius: var(--radius);
  background: #eef4ff;
  color: #13346b;
  padding: 7px 10px;
  font-size: 0.86rem;
  font-weight: 800;
}

.topic-grid,
.diagram-grid,
.fact-grid,
.resource-grid {
  display: grid;
  gap: 16px;
}

.topic-grid {
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.diagram-grid {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.fact-grid {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.resource-grid {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.topic-card,
.fact-card,
.diagram-card,
.resource-card,
.question-card,
.test-block {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: 0 10px 28px rgba(7, 17, 38, 0.06);
}

.topic-card,
.fact-card,
.resource-card {
  padding: 18px;
}

.topic-card h3,
.fact-card h3,
.resource-card h3 {
  margin: 0 0 8px;
  color: var(--blue-dark);
  font-size: 1.06rem;
}

.topic-card p,
.fact-card p,
.resource-card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
}

.topic-card ul,
.fact-card ul,
.resource-card ul,
.answer-body ul,
.question-list,
.answer-list {
  margin: 10px 0 0;
  padding-left: 20px;
}

.topic-card li,
.fact-card li,
.resource-card li,
.answer-body li,
.question-list li,
.answer-list li {
  margin: 5px 0;
}

.diagram-card {
  overflow: hidden;
}

.diagram-card figure {
  margin: 0;
}

.diagram-card img {
  width: 100%;
  background: #fff;
}

.diagram-card figcaption,
.exam-figure figcaption {
  padding: 11px 14px 13px;
  color: var(--muted);
  border-top: 1px solid var(--line);
  font-size: 0.92rem;
}

.callout {
  margin-top: 18px;
  border-left: 5px solid var(--green);
  background: #eaf8f0;
  border-radius: var(--radius);
  padding: 15px 17px;
  color: #173f32;
}

.callout strong {
  color: #063a28;
}

.source-panel {
  margin-top: 22px;
  display: grid;
  grid-template-columns: minmax(240px, 0.9fr) minmax(360px, 1.35fr);
  gap: 20px;
  align-items: center;
  background:
    radial-gradient(circle at 100% 0%, rgba(255, 204, 51, 0.18), transparent 34%),
    linear-gradient(135deg, #071126, #08245a);
  color: #eaf0ff;
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: 0 18px 46px rgba(7, 17, 38, 0.18);
  border: 1px solid rgba(255, 255, 255, 0.12);
}

.source-panel h3 {
  margin: 0 0 6px;
  color: #fff;
  font-size: 1.12rem;
}

.source-panel p {
  margin: 0;
  color: #cdd7ee;
  line-height: 1.45;
  max-width: 68ch;
}

.source-links {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
}

.source-links a {
  color: #08235f;
  background: var(--gold);
  border-radius: 10px;
  padding: 10px 12px;
  text-decoration: none;
  font-weight: 900;
  text-align: center;
  line-height: 1.2;
  box-shadow: inset 0 -2px 0 rgba(7, 17, 38, 0.12);
}

.drawing-studio {
  background:
    linear-gradient(180deg, rgba(246, 249, 255, 0.92), rgba(255, 255, 255, 1)),
    repeating-linear-gradient(0deg, transparent 0 31px, rgba(12, 79, 179, 0.06) 32px),
    repeating-linear-gradient(90deg, transparent 0 31px, rgba(12, 79, 179, 0.06) 32px);
}

.studio-guide {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  margin-bottom: 24px;
}

.studio-guide article {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 15px;
  box-shadow: 0 10px 25px rgba(7, 17, 38, 0.06);
}

.studio-guide strong,
.studio-guide span {
  display: block;
}

.studio-guide strong {
  color: var(--blue-dark);
  font-size: 1rem;
  margin-bottom: 6px;
}

.studio-guide span {
  color: var(--muted);
  font-size: 0.92rem;
  line-height: 1.45;
}

.studio-cluster {
  margin-top: 26px;
}

.studio-cluster-head {
  display: grid;
  gap: 5px;
  margin-bottom: 14px;
  border-left: 5px solid var(--green);
  padding-left: 14px;
}

.studio-cluster-head h3 {
  margin: 0;
  color: var(--blue-dark);
  font-size: 1.35rem;
}

.studio-cluster-head p {
  margin: 0;
  color: var(--muted);
}

.diagram-card.wide {
  grid-column: span 2;
}

.diagram-card figcaption strong {
  color: #172541;
}

.drawing-studio .diagram-card figure,
.post-upgrade .diagram-card figure {
  min-height: auto;
}

.teacher-steps {
  border-top: 1px solid var(--line);
  background: linear-gradient(180deg, #f8fbff, #fff);
  padding: 13px 15px 15px;
  color: #233555;
}

.teacher-steps strong {
  display: block;
  color: var(--green);
  font-size: 0.92rem;
  margin-bottom: 6px;
}

.teacher-steps ol {
  margin: 0;
  padding-left: 20px;
}

.teacher-steps li {
  margin: 5px 0;
  line-height: 1.45;
}

.post-upgrade {
  background:
    linear-gradient(180deg, #ffffff, #f4f8ff),
    repeating-linear-gradient(0deg, transparent 0 31px, rgba(12, 79, 179, 0.05) 32px);
}

.study-reference {
  margin-top: 18px;
}

.official-bank {
  margin-top: 34px;
}

.official-cluster {
  margin: 0 0 24px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
  overflow: hidden;
}

.official-cluster-head {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 14px;
  align-items: start;
  padding: 18px;
  background: #fbfcff;
  border-bottom: 1px solid var(--line);
}

.official-cluster-head h3 {
  margin: 0 0 5px;
  color: var(--blue-dark);
  font-size: 1.18rem;
}

.official-cluster-head p {
  margin: 0;
  color: var(--muted);
}

.official-cluster-head span {
  color: #08235f;
  background: var(--gold);
  border-radius: var(--radius);
  padding: 6px 9px;
  font-weight: 900;
  white-space: nowrap;
}

.official-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(170px, 1fr));
  gap: 12px;
  padding: 14px;
}

.official-card {
  margin: 0;
  border: 1px solid #e3eaf6;
  border-radius: var(--radius);
  overflow: hidden;
  background: #fff;
}

.official-card img {
  width: 100%;
  height: 165px;
  object-fit: contain;
  background: #fff;
  border-bottom: 1px solid #edf2f9;
}

.official-card figcaption {
  padding: 10px;
  display: grid;
  gap: 6px;
  color: var(--muted);
  font-size: 0.82rem;
}

.official-card figcaption strong {
  color: #1b2740;
  font-size: 0.86rem;
}

.official-card figcaption a {
  color: var(--blue);
  font-weight: 900;
  text-decoration: none;
}

.practice-panel {
  position: sticky;
  top: 77px;
  z-index: 10;
  background: rgba(247, 249, 255, 0.96);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 14px;
  margin-bottom: 22px;
  box-shadow: 0 12px 34px rgba(7, 17, 38, 0.08);
  backdrop-filter: blur(12px);
}

.practice-tools {
  display: grid;
  grid-template-columns: minmax(180px, 1fr) auto;
  gap: 12px;
  align-items: center;
}

.searchbox {
  width: 100%;
  border: 1px solid #c9d5e8;
  border-radius: var(--radius);
  padding: 12px 14px;
  font: inherit;
  background: #fff;
}

.test-jump {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.download-panel {
  margin: 0 0 24px;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
  box-shadow: 0 12px 34px rgba(7, 17, 38, 0.08);
}

.download-heading {
  margin-bottom: 14px;
}

.download-heading h3 {
  margin: 0 0 5px;
  color: var(--blue-dark);
  font-size: 1.28rem;
}

.download-heading p {
  margin: 0;
  color: var(--muted);
}

.download-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 12px;
}

.download-card {
  display: grid;
  gap: 8px;
  border: 1px solid #e3eaf6;
  border-radius: var(--radius);
  padding: 14px;
  background: #fbfcff;
}

.download-card strong {
  color: var(--blue-dark);
  font-size: 1.04rem;
}

.download-card span {
  color: var(--muted);
  font-size: 0.92rem;
}

.download-card div {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.download-card a {
  text-decoration: none;
  border-radius: var(--radius);
  padding: 8px 10px;
  background: var(--blue);
  color: #fff;
  font-weight: 900;
  font-size: 0.9rem;
}

.download-card a + a {
  background: var(--green);
}

.objective-test {
  background: transparent;
}

.objective-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 14px;
  padding: 16px;
}

.objective-card {
  display: grid;
  gap: 12px;
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: 0 10px 28px rgba(7, 17, 38, 0.06);
  overflow: hidden;
}

.objective-top {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 10px;
  align-items: start;
  padding: 14px 14px 0;
}

.objective-top span {
  background: var(--gold);
  color: var(--blue-dark);
  border-radius: var(--radius);
  padding: 5px 8px;
  font-weight: 900;
}

.objective-top p {
  margin: 2px 0 0;
  color: var(--blue-dark);
  font-weight: 900;
}

.option-list {
  margin: 0;
  padding: 0 14px 0 38px;
  color: #24304a;
}

.option-list li {
  margin: 6px 0;
}

.objective-answer {
  border-top: 1px solid var(--line);
  background: #fcfffd;
}

.objective-answer .answer-body p {
  margin: 0 0 8px;
}

.test-block {
  margin: 0 0 24px;
  overflow: hidden;
}

.test-header {
  background: linear-gradient(135deg, var(--blue-dark), var(--blue));
  color: #fff;
  padding: 22px;
}

.test-header h3 {
  margin: 0 0 6px;
  font-size: 1.5rem;
}

.test-header p {
  margin: 0;
  color: #eaf0ff;
}

.question-card {
  margin: 16px;
  padding: 0;
  overflow: hidden;
}

.question-title {
  display: flex;
  gap: 12px;
  align-items: flex-start;
  justify-content: space-between;
  padding: 16px 18px;
  border-bottom: 1px solid var(--line);
  background: #fbfcff;
}

.question-title h4 {
  margin: 0;
  color: var(--blue-dark);
  font-size: 1.08rem;
}

.question-title span {
  display: inline-flex;
  min-width: 46px;
  justify-content: center;
  border-radius: var(--radius);
  background: var(--gold);
  color: #08235f;
  padding: 5px 8px;
  font-weight: 900;
  font-size: 0.88rem;
}

.question-body {
  padding: 18px;
}

.question-list,
.answer-list {
  list-style: none;
  padding-left: 0;
}

.question-list li,
.answer-list li {
  display: grid;
  grid-template-columns: minmax(42px, auto) minmax(0, 1fr);
  gap: 10px;
  align-items: start;
  border-bottom: 1px solid #eef2f8;
  padding: 8px 0;
}

.question-list li:last-child,
.answer-list li:last-child {
  border-bottom: 0;
}

.label {
  font-weight: 900;
  color: var(--blue);
}

.answer-list .label {
  color: var(--green);
}

.exam-figure {
  margin: 14px 0;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow: hidden;
  background: #fff;
}

.exam-figure img {
  width: 100%;
  max-height: 560px;
  object-fit: contain;
  background: #fff;
}

details.answer-box {
  border-top: 1px solid var(--line);
  background: #fcfffd;
}

details.answer-box summary {
  cursor: pointer;
  padding: 14px 18px;
  font-weight: 900;
  color: #063a28;
  list-style: none;
}

details.answer-box summary::-webkit-details-marker {
  display: none;
}

details.answer-box summary::after {
  content: "+";
  float: right;
  color: var(--green);
  font-weight: 900;
}

details.answer-box[open] summary::after {
  content: "-";
}

.answer-body {
  padding: 0 18px 18px;
}

.note-strip {
  margin: 12px 0 0;
  padding: 12px 14px;
  border-radius: var(--radius);
  background: #fff8dd;
  color: #5a4100;
  border: 1px solid #f2d76a;
}

.footer {
  background:
    radial-gradient(circle at 12% 0%, rgba(255, 204, 51, 0.22), transparent 28%),
    linear-gradient(135deg, #06122d 0%, #08245a 48%, #041024 100%);
  color: #dbe6ff;
  padding: 42px 0 18px;
}

.footer-inner {
  width: min(var(--max), calc(100% - 32px));
  margin: 0 auto;
  display: grid;
  grid-template-columns: 1.35fr 0.9fr 1fr;
  gap: 22px;
  align-items: stretch;
}

.footer-showcase > * {
  border: 1px solid rgba(255, 255, 255, 0.18);
  background: rgba(255, 255, 255, 0.075);
  box-shadow: 0 18px 46px rgba(0, 0, 0, 0.22);
}

.footer-brand-block,
.footer-focus,
.footer-contact-card {
  border-radius: var(--radius);
  padding: 18px;
}

.footer-brand-block {
  display: grid;
  grid-template-columns: 76px minmax(0, 1fr);
  gap: 16px;
  align-items: start;
}

.footer-brand-block img {
  width: 76px;
  height: 76px;
  object-fit: contain;
  border-radius: 14px;
  background: #fff;
  padding: 6px;
}

.footer strong,
.footer h3 {
  color: #fff;
}

.footer-brand-block strong {
  display: block;
  font-size: 1.32rem;
  line-height: 1.1;
}

.footer-brand-block span {
  display: block;
  margin-top: 4px;
  color: var(--gold);
  font-weight: 900;
}

.footer p {
  margin: 9px 0 0;
  color: #d5def4;
  line-height: 1.55;
}

.footer h3 {
  margin: 0 0 12px;
  font-size: 1.05rem;
}

.footer-focus ul {
  margin: 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 10px;
}

.footer-focus li {
  position: relative;
  padding-left: 18px;
  color: #e8efff;
  line-height: 1.4;
}

.footer-focus li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.55em;
  width: 8px;
  height: 8px;
  border-radius: 999px;
  background: var(--gold);
}

.contact-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.contact-list a {
  color: #06122d;
  background: linear-gradient(180deg, #ffe680, var(--gold));
  border-radius: 10px;
  padding: 10px 12px;
  text-decoration: none;
  font-weight: 900;
  text-align: center;
}

.footer-bottom {
  width: min(var(--max), calc(100% - 32px));
  margin: 18px auto 0;
  padding-top: 14px;
  border-top: 1px solid rgba(255, 255, 255, 0.18);
  display: flex;
  justify-content: space-between;
  gap: 14px;
  color: #b9c7e8;
  font-weight: 800;
  flex-wrap: wrap;
}

.learning-ambience,
.advertorial-strip {
  width: min(var(--max), calc(100% - 28px));
  margin: 18px auto 0;
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 14px;
}

.learning-ambience figure,
.advertorial-strip figure,
.diagram-card figure,
.pdf-viewer-card,
.interaction-panel,
.interaction-rules {
  border: 1px solid rgba(12, 79, 179, 0.16);
  border-radius: var(--radius);
  background: #fff;
  box-shadow: 0 14px 36px rgba(7, 17, 38, 0.08);
}

.learning-ambience figure,
.advertorial-strip figure {
  margin: 0;
  overflow: hidden;
}

.learning-ambience img,
.advertorial-strip img {
  width: 100%;
  height: 170px;
  object-fit: contain;
  background: linear-gradient(180deg, #f7fbff, #fff);
  padding: 8px;
  display: block;
}

.learning-ambience figcaption,
.advertorial-strip figcaption {
  text-align: center;
  padding: 9px 10px;
  color: var(--blue-dark);
  font-weight: 900;
  font-size: 0.9rem;
  border-top: 1px solid var(--line);
}

.eq {
  font-family: Cambria Math, "Times New Roman", serif;
  font-size: 1.06em;
  color: #071126;
  white-space: normal;
}

.formula-section {
  margin-top: 24px;
}

.formula-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 14px;
}

.formula-card {
  background: #fff;
  border: 1px solid rgba(12, 79, 179, 0.16);
  border-left: 5px solid var(--blue);
  border-radius: var(--radius);
  padding: 16px;
  box-shadow: 0 10px 28px rgba(7, 17, 38, 0.06);
}

.formula-card h3 {
  margin: 0 0 10px;
  color: var(--blue-dark);
  font-size: 1rem;
}

.formula-card dl {
  margin: 0;
  display: grid;
  gap: 7px;
}

.formula-card dt {
  color: var(--green);
  font-weight: 900;
}

.formula-card dd {
  margin: -4px 0 6px;
  color: #263650;
  line-height: 1.45;
}

.conversion-strip {
  margin-top: 14px;
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
  background: #071126;
  color: #eaf0ff;
  border-radius: var(--radius);
  padding: 12px;
}

.conversion-strip span {
  background: rgba(255, 255, 255, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.16);
  border-radius: var(--radius);
  padding: 6px 8px;
  font-weight: 800;
}

.diagram-card {
  display: grid;
  align-content: stretch;
}

.diagram-card figure {
  min-height: 100%;
  display: grid;
  grid-template-rows: minmax(260px, auto) auto;
}

.diagram-card img {
  display: block;
  width: 100%;
  height: 100%;
  max-height: 520px;
  object-fit: contain;
  object-position: center;
  padding: 12px;
  background:
    linear-gradient(180deg, #fbfdff, #fff),
    repeating-linear-gradient(0deg, transparent 0 31px, rgba(12, 79, 179, 0.05) 32px);
}

.diagram-card.wide img {
  max-height: 640px;
}

.compact-diagrams .diagram-card img {
  max-height: 380px;
}

.pdf-viewer-card {
  overflow: hidden;
  padding: 10px;
}

.pdf-viewer-card object {
  width: 100%;
  height: min(760px, 78vh);
  display: block;
  border: 0;
  border-radius: var(--radius);
  background: #f7f9ff;
}

.interaction-shell {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: 18px;
  align-items: start;
}

.interaction-panel,
.interaction-rules {
  padding: 18px;
}

.comment-form {
  display: grid;
  gap: 12px;
}

.comment-form label {
  display: grid;
  gap: 7px;
  color: #1d2a42;
  font-weight: 900;
}

.comment-form textarea,
.reply-box input {
  width: 100%;
  border: 1px solid #bfd0ee;
  border-radius: var(--radius);
  padding: 11px 12px;
  font: inherit;
  background: #fff;
}

.comment-tools {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
  justify-content: space-between;
}

.file-picker {
  border: 1px dashed #9ab2d8;
  background: #f7fbff;
  border-radius: var(--radius);
  padding: 10px;
  color: var(--blue-dark);
}

.comment-tools button,
.reply-box button,
.reaction-row button,
.comment-admin-actions button,
.reply-card button {
  border: 0;
  border-radius: var(--radius);
  padding: 8px 10px;
  font: inherit;
  font-weight: 900;
  cursor: pointer;
}

.comment-tools button,
.reply-box button {
  background: var(--green);
  color: #fff;
}

.comment-status {
  min-height: 22px;
  margin: 0;
  color: var(--green);
  font-weight: 900;
}

.comment-status.error {
  color: #b92323;
}

.comment-list {
  display: grid;
  gap: 14px;
  margin-top: 18px;
}

.empty-comments,
.comment-card {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fbfcff;
  padding: 14px;
}

.comment-head {
  display: flex;
  gap: 12px;
  align-items: flex-start;
  justify-content: space-between;
}

.comment-head strong,
.reply-card strong {
  color: var(--blue-dark);
}

.comment-head span,
.reply-card span {
  display: block;
  color: var(--muted);
  font-size: 0.86rem;
}

.comment-admin-actions,
.reaction-row,
.reply-box {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.comment-admin-actions button {
  background: #ffe9e9;
  color: #8c1f1f;
}

.reaction-row button {
  background: #eef4ff;
  color: #17345f;
}

.reaction-row button span {
  background: #fff;
  border-radius: 999px;
  padding: 1px 6px;
  margin-left: 3px;
}

.reply-box {
  margin-top: 12px;
  align-items: center;
}

.reply-box input {
  flex: 1 1 280px;
}

.reply-list {
  display: grid;
  gap: 8px;
  margin-top: 12px;
  padding-left: 14px;
  border-left: 3px solid #dce7f8;
}

.reply-card {
  background: #fff;
  border: 1px solid #e4ebf6;
  border-radius: var(--radius);
  padding: 10px;
}

.comment-attachment {
  margin: 10px 0;
  border: 1px solid #dce7f8;
  border-radius: var(--radius);
  overflow: hidden;
  background: #fff;
}

.comment-attachment img {
  display: block;
  max-height: 260px;
  width: 100%;
  object-fit: contain;
  background: #fff;
}

.comment-attachment figcaption,
.comment-file {
  padding: 8px 10px;
  color: var(--muted);
}

.comment-banned {
  border-color: #e7b8b8;
  background: #fff8f8;
}

.interaction-rules h3 {
  margin-top: 0;
  color: var(--blue-dark);
}

.hidden {
  display: none !important;
}

@media (max-width: 940px) {
  .topbar-inner,
  .hero-inner,
  .footer-inner,
  .practice-tools,
  .section-heading,
  .source-panel,
  .studio-guide,
  .interaction-shell {
    grid-template-columns: 1fr;
  }

  .hero-inner {
    padding-top: 34px;
  }

  .nav,
  .test-jump,
  .contact-list,
  .source-links {
    justify-content: flex-start;
  }

  .topic-grid,
  .diagram-grid,
  .fact-grid,
  .resource-grid,
  .formula-grid,
  .security-grid,
  .learning-ambience,
  .advertorial-strip {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 640px) {
  .topbar {
    position: static;
  }

  .topbar-inner {
    width: min(var(--max), calc(100% - 22px));
    padding: 12px 0;
  }

  .nav {
    width: 100%;
  }

  .nav a {
    flex: 1 1 auto;
    text-align: center;
  }

  .section,
  .hero-inner,
  .footer-inner {
    width: min(var(--max), calc(100% - 22px));
  }

  .topic-grid,
  .diagram-grid,
  .fact-grid,
  .resource-grid,
  .official-grid,
  .objective-grid,
  .formula-grid,
  .security-grid,
  .learning-ambience,
  .advertorial-strip,
  .credential-grid {
    grid-template-columns: 1fr;
  }

  .diagram-card.wide {
    grid-column: auto;
  }

  .practice-panel {
    position: static;
  }

  .question-list li,
  .answer-list li {
    grid-template-columns: 1fr;
  }
}

@media print {
  .topbar,
  .practice-panel,
  .download-panel,
  .hero-actions,
  .footer {
    display: none;
  }

  body {
    background: #fff;
    color: #000;
  }

  .hero {
    background: #fff;
    color: #000;
  }

  .hero-inner,
  .section {
    width: 100%;
    padding: 18px 0;
  }

  .test-block,
  .question-card,
  .topic-card,
  .fact-card,
  .diagram-card {
    box-shadow: none;
    break-inside: avoid;
  }

  details.answer-box {
    display: block;
  }

  details.answer-box summary {
    display: none;
  }
}