:root {
  --ink: #eef5fb;
  --muted: #c7d3e2;
  --paper: #07111d;
  --surface: #0e1b2b;
  --surface-2: #132338;
  --line: #24364d;
  --navy: #8bbbe8;
  --navy-2: #06101c;
  --green: #42bd91;
  --green-soft: rgba(66, 189, 145, 0.14);
  --gold: #d9aa51;
  --red: #f07171;
  --shadow: 0 18px 45px rgba(0, 0, 0, 0.34);
  --radius: 8px;
}

body[data-theme="light"] {
  --ink: #102033;
  --muted: #4c5d70;
  --paper: #f3f7fb;
  --surface: #ffffff;
  --surface-2: #eaf1f8;
  --line: #c9d5e3;
  --navy: #17385f;
  --navy-2: #dfe9f4;
  --green: #247a61;
  --green-soft: rgba(36, 122, 97, 0.12);
  --gold: #9a6c1e;
  --red: #b63f3f;
  --shadow: 0 18px 45px rgba(28, 45, 68, 0.12);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background:
    radial-gradient(circle at 20% 0%, rgba(66, 189, 145, 0.1), transparent 30rem),
    var(--paper);
  font-family:
    Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
    sans-serif;
  font-size: 16px;
  line-height: 1.7;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}

body[data-theme="light"] {
  background:
    radial-gradient(circle at 18% 0%, rgba(36, 122, 97, 0.12), transparent 30rem),
    var(--paper);
}

a {
  color: inherit;
  text-decoration: none;
}

button {
  font: inherit;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  min-height: 72px;
  padding: 12px clamp(18px, 4vw, 56px);
  color: #ffffff;
  background: rgba(6, 16, 28, 0.96);
  border-bottom: 1px solid rgba(255, 255, 255, 0.12);
  backdrop-filter: blur(16px);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
}

.brand-mark {
  display: grid;
  place-items: center;
  width: 42px;
  height: 42px;
  color: #0f2846;
  background: #ffffff;
  border-radius: 8px;
  font-weight: 800;
}

.brand strong,
.brand small {
  display: block;
}

.brand strong {
  font-size: 16px;
  line-height: 1.2;
}

.brand small {
  color: rgba(255, 255, 255, 0.84);
  font-size: 13px;
}

.top-nav {
  display: flex;
  align-items: center;
  gap: 8px;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}

.top-nav a {
  padding: 9px 12px;
  color: rgba(255, 255, 255, 0.9);
  border-radius: 7px;
  font-size: 15px;
  font-weight: 700;
}

.top-nav a:hover,
.top-nav a:focus-visible {
  color: #ffffff;
  background: rgba(255, 255, 255, 0.12);
  outline: none;
}

.theme-toggle,
.translate-toggle {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  min-height: 40px;
  padding: 0 12px;
  color: #ffffff;
  background: rgba(255, 255, 255, 0.1);
  border: 1px solid rgba(255, 255, 255, 0.18);
  border-radius: 7px;
  cursor: pointer;
  font-size: 14px;
  font-weight: 800;
  transition:
    transform 160ms ease,
    background 160ms ease,
    border-color 160ms ease;
  white-space: nowrap;
}

.theme-toggle:hover,
.theme-toggle:focus-visible,
.translate-toggle:hover,
.translate-toggle:focus-visible {
  transform: translateY(-1px);
  background: rgba(255, 255, 255, 0.16);
  border-color: rgba(255, 255, 255, 0.34);
  outline: none;
}

.theme-toggle svg {
  width: 18px;
  height: 18px;
  fill: currentColor;
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(320px, 520px);
  gap: clamp(28px, 5vw, 72px);
  align-items: center;
  min-height: calc(100svh - 72px);
  padding: clamp(42px, 8vw, 92px) clamp(18px, 5vw, 72px);
  color: #ffffff;
  background:
    radial-gradient(circle at 78% 20%, rgba(66, 189, 145, 0.58), transparent 34%),
    linear-gradient(135deg, #06101c, #102844 52%, #18384d);
}

body[data-theme="light"] .site-header {
  color: #102033;
  background: rgba(255, 255, 255, 0.94);
  border-bottom-color: rgba(16, 32, 51, 0.12);
}

body[data-theme="light"] .brand-mark {
  color: #ffffff;
  background: #17385f;
}

body[data-theme="light"] .brand small,
body[data-theme="light"] .top-nav a {
  color: rgba(16, 32, 51, 0.78);
}

body[data-theme="light"] .top-nav a:hover,
body[data-theme="light"] .top-nav a:focus-visible {
  color: #102033;
  background: rgba(23, 56, 95, 0.08);
}

body[data-theme="light"] .theme-toggle {
  color: #17385f;
  background: rgba(23, 56, 95, 0.08);
  border-color: rgba(23, 56, 95, 0.18);
}

body[data-theme="light"] .translate-toggle {
  color: #17385f;
  background: rgba(23, 56, 95, 0.08);
  border-color: rgba(23, 56, 95, 0.18);
}

body[data-theme="light"] .hero {
  color: #ffffff;
  background:
    radial-gradient(circle at 78% 20%, rgba(36, 122, 97, 0.42), transparent 34%),
    linear-gradient(135deg, #17385f, #23506f 52%, #2a766c);
}

body[data-theme="light"] .hero p:not(.course-label) {
  color: rgba(255, 255, 255, 0.94);
}

.hero-copy {
  max-width: 720px;
}

.course-label {
  margin: 0 0 10px;
  color: var(--green);
  font-size: 14px;
  font-weight: 800;
  letter-spacing: 0;
  text-transform: uppercase;
}

.hero .course-label {
  color: #b9e4d6;
}

.hero h1,
.quiz-heading h2,
.practice-panel h2 {
  margin: 0;
  line-height: 1.05;
  letter-spacing: 0;
}

.hero h1 {
  max-width: 760px;
  font-size: clamp(42px, 7vw, 78px);
}

.hero p:not(.course-label) {
  max-width: 640px;
  margin: 22px 0 0;
  color: rgba(255, 255, 255, 0.92);
  font-size: clamp(18px, 2vw, 21px);
  line-height: 1.65;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 34px;
}

.primary-action,
.secondary-action,
.tool-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  padding: 0 18px;
  border: 0;
  border-radius: 7px;
  cursor: pointer;
  font-size: 15px;
  font-weight: 800;
  transition:
    transform 160ms ease,
    background 160ms ease,
    color 160ms ease,
    border-color 160ms ease;
}

.primary-action,
.tool-button {
  color: #ffffff;
  background: var(--green);
}

.secondary-action,
.tool-button.ghost {
  color: #ffffff;
  background: transparent;
  border: 1px solid rgba(255, 255, 255, 0.35);
}

.tool-button.ghost {
  color: var(--ink);
  border-color: var(--line);
}

body[data-theme="light"] .secondary-action {
  color: #ffffff;
  border-color: rgba(255, 255, 255, 0.42);
}

.primary-action:hover,
.secondary-action:hover,
.tool-button:hover {
  transform: translateY(-1px);
}

.hero-visual {
  position: relative;
  min-height: 520px;
  border: 1px solid rgba(255, 255, 255, 0.18);
  border-radius: 8px;
  background:
    linear-gradient(rgba(255, 255, 255, 0.055) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, 0.055) 1px, transparent 1px),
    rgba(255, 255, 255, 0.08);
  background-size: 38px 38px;
  box-shadow: 0 28px 70px rgba(0, 0, 0, 0.24);
  overflow: hidden;
}

.hero-visual::before,
.hero-visual::after {
  content: "";
  position: absolute;
  inset: 75px;
  border: 1px dashed rgba(255, 255, 255, 0.28);
  border-radius: 50%;
}

.hero-visual::after {
  inset: 128px;
}

.spectrum-center {
  position: absolute;
  top: 50%;
  left: 50%;
  display: grid;
  place-items: center;
  width: 168px;
  height: 168px;
  padding: 18px;
  color: var(--ink);
  background: #102033;
  border-radius: 50%;
  transform: translate(-50%, -50%);
  text-align: center;
  box-shadow: var(--shadow);
}

body[data-theme="light"] .spectrum-center,
body[data-theme="light"] .orbit-item {
  color: #ffffff;
  background: #102033;
}

.spectrum-center span,
.orbit-item span {
  color: #d4deeb;
  font-size: 13px;
  font-weight: 800;
}

.spectrum-center strong {
  font-size: 22px;
  line-height: 1.05;
}

.orbit-item {
  position: absolute;
  width: 160px;
  padding: 14px;
  color: var(--ink);
  background: #102033;
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.orbit-item strong {
  font-size: 17px;
}

.orbit-item strong,
.orbit-item span {
  display: block;
}

.orbit-item.people {
  top: 42px;
  left: 50%;
  transform: translateX(-50%);
  border-color: rgba(217, 170, 81, 0.72);
}

body[data-theme="light"] .spectrum-center span,
body[data-theme="light"] .orbit-item span {
  color: #d4deeb;
}

.orbit-item.product {
  right: 28px;
  top: 50%;
  transform: translateY(-50%);
}

.orbit-item.process {
  bottom: 42px;
  left: 50%;
  transform: translateX(-50%);
}

.orbit-item.project {
  left: 28px;
  top: 50%;
  transform: translateY(-50%);
}

.overview {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1px;
  margin: 0 clamp(18px, 5vw, 72px);
  transform: translateY(-36px);
  background: var(--line);
  border-radius: 8px;
  overflow: hidden;
  box-shadow: var(--shadow);
}

.overview div {
  padding: 24px;
  background: var(--surface);
}

.metric-number,
.metric-label {
  display: block;
}

.metric-number {
  color: var(--navy);
  font-size: 32px;
  font-weight: 850;
  line-height: 1;
}

.metric-label {
  margin-top: 6px;
  color: var(--muted);
  font-size: 15px;
  font-weight: 800;
}

.study-layout {
  display: grid;
  grid-template-columns: 270px minmax(0, 1fr);
  gap: 28px;
  align-items: start;
  padding: 18px clamp(18px, 5vw, 72px) 80px;
}

.lesson-nav {
  position: sticky;
  top: 96px;
  padding: 18px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: 0 10px 30px rgba(28, 45, 68, 0.06);
}

.lesson-nav h2 {
  margin: 0 0 12px;
  font-size: 18px;
}

.lesson-link {
  display: block;
  padding: 11px 9px;
  color: var(--muted);
  border-radius: 6px;
  font-size: 15px;
  font-weight: 750;
  line-height: 1.45;
}

.lesson-link:hover,
.lesson-link:focus-visible {
  color: var(--ink);
  background: var(--green-soft);
  outline: none;
}

.lesson-stack {
  display: grid;
  gap: 18px;
}

.lesson-card {
  padding: clamp(22px, 3vw, 34px);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: 0 10px 30px rgba(28, 45, 68, 0.055);
}

.lesson-head {
  display: grid;
  grid-template-columns: 52px minmax(0, 1fr);
  gap: 16px;
  align-items: start;
}

.lesson-number {
  display: grid;
  place-items: center;
  width: 52px;
  height: 52px;
  color: #ffffff;
  background: #17385f;
  border-radius: 8px;
  font-weight: 850;
}

.lesson-card h2 {
  margin: 0;
  color: var(--navy);
  font-size: clamp(24px, 4vw, 34px);
  line-height: 1.1;
}

.lesson-card .summary {
  margin: 12px 0 0;
  color: var(--muted);
  font-size: 17px;
  line-height: 1.72;
  max-width: 78ch;
}

.point-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
  margin-top: 22px;
}

.point {
  padding: 16px;
  background: var(--surface-2);
  border: 1px solid var(--line);
  border-radius: 7px;
  font-size: 16px;
  line-height: 1.6;
}

.exam-focus {
  margin-top: 20px;
  padding: 14px 16px;
  color: #dff7ef;
  background: var(--green-soft);
  border: 1px solid rgba(66, 189, 145, 0.35);
  border-radius: 7px;
  font-size: 16px;
  line-height: 1.58;
  font-weight: 800;
}

.mini-questions {
  margin-top: 20px;
  border-top: 1px solid var(--line);
  padding-top: 18px;
}

.mini-questions h3 {
  margin: 0 0 10px;
  font-size: 19px;
}

.mini-questions ol {
  margin: 0;
  padding-left: 20px;
}

.mini-questions li {
  margin: 8px 0;
  color: #e8f0f8;
  font-size: 16px;
  line-height: 1.62;
}

.practice-panel,
.quiz-section {
  margin: 0 clamp(18px, 5vw, 72px) 80px;
  padding: clamp(24px, 4vw, 42px);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.practice-panel {
  display: grid;
  grid-template-columns: 0.85fr 1.15fr;
  gap: 28px;
  align-items: start;
}

.practice-panel h2,
.quiz-heading h2 {
  color: var(--navy);
  font-size: clamp(28px, 5vw, 46px);
}

.practice-panel p:not(.course-label) {
  color: var(--muted);
  font-size: 17px;
  line-height: 1.72;
}

.review-grid {
  display: grid;
  gap: 10px;
}

.review-item {
  display: grid;
  grid-template-columns: 34px minmax(0, 1fr);
  gap: 12px;
  align-items: start;
  padding: 14px;
  background: var(--surface-2);
  border-radius: 7px;
}

.review-index {
  display: grid;
  place-items: center;
  width: 34px;
  height: 34px;
  color: #ffffff;
  background: var(--green);
  border-radius: 7px;
  font-weight: 800;
}

.review-item strong {
  display: block;
  color: var(--ink);
}

.review-item span {
  color: var(--muted);
  font-size: 15px;
  line-height: 1.55;
}

.quiz-heading {
  display: flex;
  align-items: start;
  justify-content: space-between;
  gap: 18px;
  margin-bottom: 22px;
}

.score-box {
  min-width: 132px;
  padding: 14px 16px;
  text-align: center;
  color: #ffffff;
  background: #17385f;
  border-radius: 8px;
}

.score-box span,
.score-box small {
  display: block;
}

.score-box span {
  font-size: 24px;
  font-weight: 850;
  line-height: 1;
}

.score-box small {
  margin-top: 5px;
  color: rgba(255, 255, 255, 0.86);
  font-size: 13px;
  font-weight: 700;
}

.quiz-tools {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-bottom: 20px;
}

.quiz-tools-bottom {
  justify-content: flex-end;
  margin-top: 22px;
  margin-bottom: 0;
  padding-top: 18px;
  border-top: 1px solid var(--line);
}

.question-list {
  display: grid;
  gap: 14px;
}

.question-card {
  padding: 20px;
  background: var(--surface-2);
  border: 1px solid var(--line);
  border-radius: 8px;
}

.question-card.correct {
  border-color: rgba(66, 189, 145, 0.72);
  background: rgba(66, 189, 145, 0.12);
}

.question-card.incorrect {
  border-color: rgba(240, 113, 113, 0.72);
  background: rgba(240, 113, 113, 0.12);
}

body[data-theme="light"] .question-card.correct {
  background: rgba(36, 122, 97, 0.1);
}

body[data-theme="light"] .question-card.incorrect {
  background: rgba(182, 63, 63, 0.1);
}

body[data-theme="light"] .exam-focus {
  color: #174d40;
}

body[data-theme="light"] .mini-questions li,
body[data-theme="light"] .question-title {
  color: #102033;
}

body[data-theme="light"] .answer-note {
  color: #4c5d70;
}

.question-title {
  margin: 0 0 12px;
  color: #f3f8fd;
  font-size: 17px;
  line-height: 1.62;
  font-weight: 800;
}

.option {
  display: flex;
  gap: 10px;
  align-items: flex-start;
  margin: 8px 0;
  padding: 12px 14px;
  background: #0a1726;
  border: 1px solid var(--line);
  border-radius: 7px;
  cursor: pointer;
  color: #edf4fb;
  font-size: 16px;
  line-height: 1.5;
}

body[data-theme="light"] .option {
  color: #102033;
  background: #ffffff;
}

.option input {
  margin-top: 4px;
}

.answer-note {
  display: none;
  margin-top: 12px;
  color: #d7e3ef;
  font-size: 15px;
  line-height: 1.55;
  font-weight: 700;
}

.question-card.correct .answer-note,
.question-card.incorrect .answer-note {
  display: block;
}

.site-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding: 28px clamp(18px, 5vw, 72px);
  color: rgba(255, 255, 255, 0.9);
  background: var(--navy-2);
  font-size: 15px;
}

body[data-theme="light"] .site-footer {
  color: #102033;
  background: #ffffff;
  border-top: 1px solid var(--line);
}

body[data-theme="light"] .designer-name {
  background: linear-gradient(90deg, #17385f, #247a61, #9a6c1e, #17385f);
  background-size: 260% 100%;
  text-shadow: 0 0 14px rgba(36, 122, 97, 0.22);
}

body[data-theme="light"] .social-links a {
  color: #174d40;
  background: rgba(36, 122, 97, 0.09);
  border-color: rgba(36, 122, 97, 0.24);
}

.site-footer p {
  margin: 0;
}

.designer {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  justify-content: flex-end;
  gap: 14px;
  color: var(--ink);
  font-weight: 800;
}

.designer-name {
  color: #dff7ef;
  background: linear-gradient(90deg, #dff7ef, #42bd91, #d9aa51, #8bbbe8, #dff7ef);
  background-size: 260% 100%;
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  text-shadow: 0 0 16px rgba(66, 189, 145, 0.32);
  animation: designer-gradient 8s ease-in-out infinite, designer-glow 5.5s ease-in-out infinite;
}

.social-links {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.social-links a {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  min-height: 38px;
  padding: 0 12px;
  color: #dff7ef;
  background: rgba(66, 189, 145, 0.12);
  border: 1px solid rgba(66, 189, 145, 0.32);
  border-radius: 7px;
  font-size: 14px;
  font-weight: 800;
}

.social-links a:hover,
.social-links a:focus-visible {
  color: #ffffff;
  background: rgba(66, 189, 145, 0.22);
  outline: none;
}

.social-links svg {
  width: 18px;
  height: 18px;
  fill: currentColor;
  flex: 0 0 auto;
}

@media (prefers-reduced-motion: no-preference) {
  .orbit-item {
    animation: soft-float 5s ease-in-out infinite;
  }

  .orbit-item.product,
  .orbit-item.project {
    animation-delay: 700ms;
  }
}

@keyframes soft-float {
  0%,
  100% {
    margin-top: 0;
  }
  50% {
    margin-top: -8px;
  }
}

@keyframes designer-gradient {
  0%,
  100% {
    background-position: 0% 50%;
  }
  50% {
    background-position: 100% 50%;
  }
}

@keyframes designer-glow {
  0%,
  100% {
    filter: drop-shadow(0 0 4px rgba(66, 189, 145, 0.24));
  }
  50% {
    filter: drop-shadow(0 0 12px rgba(217, 170, 81, 0.34));
  }
}

@media (prefers-reduced-motion: reduce) {
  .designer-name {
    animation: none;
    background-position: 50% 50%;
  }
}

@media (max-width: 980px) {
  .hero,
  .study-layout,
  .practice-panel {
    grid-template-columns: 1fr;
  }

  .hero {
    min-height: auto;
  }

  .lesson-nav {
    position: static;
  }

  .lesson-nav #lessonLinks {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 4px;
  }
}

@media (max-width: 700px) {
  .site-header,
  .quiz-heading,
  .site-footer {
    align-items: stretch;
    flex-direction: column;
  }

  .designer {
    justify-content: flex-start;
  }

  .header-actions {
    align-items: flex-start;
    flex-direction: column;
  }

  .top-nav {
    overflow-x: auto;
    padding-bottom: 2px;
  }

  .hero-visual {
    min-height: 500px;
  }

  .spectrum-center {
    width: 126px;
    height: 126px;
  }

  .spectrum-center strong {
    font-size: 18px;
  }

  .spectrum-center span,
  .orbit-item span {
    font-size: 11px;
  }

  .orbit-item {
    width: 122px;
    padding: 12px;
  }

  .orbit-item.product {
    right: 10px;
  }

  .orbit-item.project {
    left: 10px;
  }

  .overview,
  .point-grid,
  .lesson-nav #lessonLinks {
    grid-template-columns: 1fr;
  }

  .overview {
    transform: none;
    margin-top: 18px;
  }

  .study-layout {
    padding-top: 28px;
  }

  .lesson-head {
    grid-template-columns: 1fr;
  }
}