:root {
  --bg: #081218;
  --bg-deep: #050b10;
  --surface: rgba(11, 27, 35, 0.88);
  --surface-strong: rgba(16, 37, 48, 0.95);
  --surface-soft: rgba(20, 47, 61, 0.72);
  --text: #eef7f8;
  --muted: #a8c1c6;
  --line: rgba(129, 176, 182, 0.22);
  --accent: #4fd6c2;
  --accent-warm: #ffb866;
  --accent-hot: #ff816e;
  --shadow: 0 28px 60px rgba(0, 0, 0, 0.28);
  --radius-lg: 28px;
  --radius-md: 20px;
  --radius-sm: 14px;
  --max-width: 1180px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(circle at top left, rgba(79, 214, 194, 0.18), transparent 28rem),
    radial-gradient(circle at 86% 10%, rgba(255, 184, 102, 0.15), transparent 24rem),
    linear-gradient(180deg, #0a171e 0%, var(--bg) 36%, var(--bg-deep) 100%);
  color: var(--text);
  font-family: "Source Sans 3", sans-serif;
  line-height: 1.6;
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  background:
    radial-gradient(circle at 18% 24%, rgba(255, 129, 110, 0.07), transparent 24rem),
    radial-gradient(circle at 82% 72%, rgba(79, 214, 194, 0.08), transparent 30rem);
}

a {
  color: var(--accent);
  text-decoration-thickness: 0.08em;
  text-underline-offset: 0.18em;
}

a:hover {
  color: #8eeede;
}

p,
li {
  font-size: 1.02rem;
}

code {
  padding: 0.08rem 0.32rem;
  background: rgba(79, 214, 194, 0.12);
  border-radius: 0.4rem;
  font-family: "IBM Plex Mono", monospace;
  font-size: 0.94em;
}

.course-shell {
  position: relative;
  width: min(calc(100% - 2rem), var(--max-width));
  margin: 0 auto;
  padding: 2rem 0 4rem;
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 1rem;
}

.brand,
.brand:visited {
  color: var(--text);
  text-decoration: none;
  font-family: "Space Grotesk", sans-serif;
  font-size: 1.15rem;
  font-weight: 700;
}

.topbar-links {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
}

.topbar-links a,
.topbar-links a:visited {
  color: var(--muted);
  text-decoration: none;
}

.topbar-links a:hover,
.topbar-links a[aria-current="page"] {
  color: var(--text);
}

.course-hero,
.course-section,
.phase-hero,
.lesson-section,
.course-footer {
  animation: rise 700ms ease both;
}

.course-hero,
.phase-hero {
  position: relative;
  padding: clamp(1.25rem, 3vw, 2rem);
  background:
    linear-gradient(145deg, rgba(13, 35, 45, 0.94), rgba(7, 21, 29, 0.92)),
    var(--surface);
  border: 1px solid var(--line);
  border-radius: calc(var(--radius-lg) + 4px);
  box-shadow: var(--shadow);
  overflow: hidden;
}

.course-hero::after,
.phase-hero::after {
  content: "";
  position: absolute;
  inset: auto -5rem -5rem auto;
  width: 20rem;
  height: 20rem;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(79, 214, 194, 0.22), transparent 68%);
  filter: blur(8px);
}

.hero-copy {
  position: relative;
  z-index: 1;
  max-width: 67rem;
}

.eyebrow,
.section-label,
.phase-number,
.mini-label {
  margin: 0;
  color: var(--accent-warm);
  font-family: "IBM Plex Mono", monospace;
  font-size: 0.82rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

h1,
h2,
h3 {
  font-family: "Space Grotesk", sans-serif;
}

h1 {
  max-width: 13ch;
  margin: 0.7rem 0 0;
  font-size: clamp(2.75rem, 7vw, 5.4rem);
  line-height: 0.97;
  letter-spacing: -0.04em;
}

.phase-hero h1 {
  max-width: 18ch;
}

.lead {
  max-width: 53rem;
  margin: 1.15rem 0 0;
  color: var(--muted);
  font-size: clamp(1.08rem, 2vw, 1.3rem);
}

.button-row,
.phase-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.95rem;
  margin-top: 1.8rem;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 3rem;
  padding: 0.8rem 1.2rem;
  border: 1px solid transparent;
  border-radius: 999px;
  font-weight: 700;
  text-decoration: none;
  transition:
    transform 180ms ease,
    border-color 180ms ease,
    background-color 180ms ease;
}

.button:hover {
  transform: translateY(-2px);
}

.button-primary {
  background: linear-gradient(135deg, var(--accent), #2ba6c6);
  color: #031017;
}

.button-primary:hover {
  color: #031017;
}

.button-secondary {
  border-color: rgba(255, 255, 255, 0.14);
  background: rgba(255, 255, 255, 0.04);
  color: var(--text);
}

.course-section,
.lesson-section,
.course-footer {
  margin-top: 1rem;
  padding: clamp(1.15rem, 2vw, 1.55rem);
  background: linear-gradient(180deg, rgba(10, 25, 32, 0.95), rgba(7, 18, 24, 0.95));
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow);
}

.section-heading {
  max-width: 58rem;
}

.section-heading h2,
.lesson-section h2 {
  margin: 0.2rem 0 0;
  max-width: 24ch;
  font-size: clamp(1.65rem, 3vw, 2.45rem);
  line-height: 1.05;
}

.section-heading p:last-child,
.lesson-section > p {
  max-width: 56rem;
  margin: 0.9rem 0 0;
  color: var(--muted);
}

.phase-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
  margin-top: 1.4rem;
}

.phase-card {
  display: grid;
  gap: 0.55rem;
  min-height: 13rem;
  padding: 1.15rem;
  color: var(--text);
  text-decoration: none;
  background: rgba(18, 42, 54, 0.72);
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  transition:
    transform 180ms ease,
    border-color 180ms ease,
    background-color 180ms ease;
}

.phase-card:hover,
.phase-card:focus-visible {
  color: var(--text);
  transform: translateY(-3px);
  border-color: rgba(79, 214, 194, 0.52);
  background: rgba(20, 52, 65, 0.94);
}

.phase-card strong {
  font-family: "Space Grotesk", sans-serif;
  font-size: 1.2rem;
  line-height: 1.15;
}

.phase-card span:last-child {
  color: var(--muted);
}

.course-layout {
  display: grid;
  grid-template-columns: 18rem minmax(0, 1fr);
  gap: 1rem;
  align-items: start;
  margin-top: 1rem;
}

.course-sidebar {
  position: sticky;
  top: 1rem;
  display: grid;
  gap: 1rem;
}

.sidebar-block {
  padding: 1rem;
  background: rgba(8, 24, 31, 0.78);
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
}

.sidebar-block h2 {
  margin: 0 0 0.65rem;
  font-size: 1rem;
}

.sidebar-block nav {
  display: grid;
  gap: 0.2rem;
}

.sidebar-block a {
  display: block;
  padding: 0.42rem 0;
  color: var(--muted);
  text-decoration: none;
}

.sidebar-block a:hover,
.sidebar-block a[aria-current="page"] {
  color: var(--text);
}

.lesson-list,
.concept-list,
.checklist,
.phase-points {
  display: grid;
  gap: 0.55rem;
  margin: 1rem 0 0;
  padding-left: 1.2rem;
}

.lesson-list li,
.concept-list li,
.checklist li,
.phase-points li {
  color: var(--muted);
}

.lesson-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
  margin-top: 1rem;
}

.lesson-panel,
.prompt-block {
  min-width: 0;
  padding: 1rem;
  background: var(--surface-soft);
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
}

.lesson-panel h3,
.prompt-block h3 {
  margin: 0 0 0.55rem;
  font-size: 1.08rem;
}

.lesson-panel p {
  margin: 0;
  color: var(--muted);
}

.prompt-block {
  margin-top: 1rem;
}

.prompt-block pre {
  margin: 0.8rem 0 0;
  max-width: 100%;
  padding: 0.95rem 1rem;
  overflow-x: auto;
  background: rgba(3, 12, 17, 0.82);
  border: 1px solid rgba(79, 214, 194, 0.16);
  border-radius: var(--radius-sm);
}

.prompt-block code {
  display: block;
  padding: 0;
  background: transparent;
  border-radius: 0;
  color: #d6fff8;
  line-height: 1.55;
  white-space: pre-wrap;
  word-break: break-word;
}

.phase-pager {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 1rem;
}

.phase-pager a {
  flex: 1;
  padding: 1rem;
  color: var(--text);
  text-decoration: none;
  background: rgba(18, 42, 54, 0.72);
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
}

.phase-pager a:last-child {
  text-align: right;
}

.phase-pager span {
  display: block;
  color: var(--muted);
  font-size: 0.95rem;
}

.footer-grid {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
}

.footer-brand {
  margin: 0;
  font-family: "Space Grotesk", sans-serif;
  font-size: 1.05rem;
}

.footer-copy {
  margin: 0.25rem 0 0;
  color: var(--muted);
}

.footer-links {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
}

.footer-links a {
  color: var(--muted);
  text-decoration: none;
}

.footer-links a:hover {
  color: var(--text);
}

@keyframes rise {
  from {
    opacity: 0;
    transform: translateY(18px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  .course-hero,
  .course-section,
  .phase-hero,
  .lesson-section,
  .course-footer {
    animation: none;
  }

  .button,
  .phase-card,
  .phase-pager a {
    transition: none;
  }
}

@media (max-width: 980px) {
  .phase-grid,
  .lesson-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .course-layout {
    grid-template-columns: 1fr;
  }

  .course-sidebar {
    position: static;
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 720px) {
  .course-shell {
    width: min(calc(100% - 1rem), var(--max-width));
    padding-top: 0.6rem;
  }

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

  .topbar-links {
    gap: 0.75rem;
  }

  .course-hero,
  .phase-hero,
  .course-section,
  .lesson-section,
  .course-footer {
    padding: 1rem;
  }

  h1,
  .phase-hero h1 {
    max-width: none;
  }

  .phase-grid,
  .lesson-grid,
  .course-sidebar {
    grid-template-columns: 1fr;
  }

  .phase-pager {
    flex-direction: column;
  }

  .phase-pager a:last-child {
    text-align: left;
  }

  .button-row,
  .phase-actions {
    flex-direction: column;
  }

  .button {
    width: 100%;
  }
}