:root {
  --bg: #0b0d10;
  --surface: #12151b;
  --surface-light: #191d25;
  --text-main: #f5f5f4;
  --text-muted: #a8a29e;
  --border: #2a2f3a;
  --accent: #991b1b;
  --accent-soft: rgba(153, 27, 27, 0.14);
  --accent-hover: #b91c1c;
  --code-bg: #050505;
  --code-text: #fef2f2;
  --terminal-green: #22c55e;
  --terminal-yellow: #facc15;
  --terminal-blue: #38bdf8;

  --font-sans: "Inter", system-ui, sans-serif;
  --font-mono: "JetBrains Mono", Consolas, monospace;

  --nav-height: 72px;
  --radius-sm: 10px;
  --radius-md: 16px;
  --radius-lg: 24px;
  --shadow: 0 24px 80px rgba(0, 0, 0, 0.45);
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: 100px;
}

body {
  min-height: 100vh;
  background:
    radial-gradient(circle at top left, rgba(153, 27, 27, 0.14), transparent 32rem),
    radial-gradient(circle at top right, rgba(153, 27, 27, 0.08), transparent 28rem),
    var(--bg);
  color: var(--text-main);
  font-family: var(--font-sans);
  line-height: 1.7;
  overflow-x: hidden;
}

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

button,
input,
textarea,
select {
  font: inherit;
}

button {
  cursor: pointer;
}

img,
svg {
  display: block;
}

::selection {
  background: var(--accent);
  color: white;
}

/* Accessibility */

.skip-link {
  position: fixed;
  left: 1rem;
  top: -5rem;
  z-index: 9999;
  background: var(--accent);
  color: white;
  padding: 0.7rem 1rem;
  border-radius: var(--radius-sm);
  transition: top 0.2s ease;
}

.skip-link:focus {
  top: 1rem;
}

/* Layout */

.page-container {
  width: min(1180px, calc(100% - 2rem));
  margin-inline: auto;
}

.narrow {
  width: min(820px, calc(100% - 2rem));
}

.section-padding {
  padding: 6rem 0;
}

.section-padding-small {
  padding: 3.5rem 0;
}

#scroll-progress {
  position: fixed;
  inset: 0 auto auto 0;
  width: 0%;
  height: 3px;
  background: linear-gradient(90deg, var(--accent), var(--accent-hover));
  z-index: 9999;
}

/* Header / Navbar */

.site-header {
  position: sticky;
  top: 0;
  z-index: 999;
  height: var(--nav-height);
  background: rgba(11, 13, 16, 0.88);
  backdrop-filter: blur(18px);
  border-bottom: 1px solid rgba(42, 47, 58, 0.85);
}

.navbar {
  width: min(1180px, calc(100% - 2rem));
  height: var(--nav-height);
  margin-inline: auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.5rem;
}

.nav-brand {
  display: grid;
  gap: 0.05rem;
}

.nav-logo {
  font-weight: 700;
  letter-spacing: -0.02em;
}

.nav-byline {
  color: var(--text-muted);
  font-size: 0.78rem;
}

.nav-menu {
  display: flex;
  align-items: center;
  gap: 1.15rem;
}

.nav-link {
  color: var(--text-muted);
  font-size: 0.92rem;
  transition: color 0.2s ease;
}

.nav-link:hover,
.nav-link:focus-visible {
  color: var(--text-main);
}

.github-link,
.footer-github {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  color: var(--text-muted);
  transition: color 0.2s ease, transform 0.2s ease;
}

.github-link:hover,
.footer-github:hover {
  color: var(--text-main);
  transform: translateY(-1px);
}

.github-icon {
  width: 22px;
  height: 22px;
  fill: currentColor;
}

.language-switcher {
  display: inline-flex;
  align-items: center;
  padding: 0.18rem;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: var(--surface);
}

.language-button {
  border: 0;
  color: var(--text-muted);
  background: transparent;
  padding: 0.35rem 0.65rem;
  border-radius: 999px;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  transition: all 0.2s ease;
}

.language-button.active {
  background: var(--accent);
  color: white;
}

.mobile-menu-button {
  display: none;
  width: 42px;
  height: 42px;
  border: 1px solid var(--border);
  background: var(--surface);
  border-radius: var(--radius-sm);
  align-items: center;
  justify-content: center;
  flex-direction: column;
  gap: 5px;
}

.mobile-menu-button span {
  width: 18px;
  height: 2px;
  background: var(--text-main);
  border-radius: 999px;
}

/* Buttons */

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  padding: 0.75rem 1.05rem;
  border-radius: 999px;
  font-weight: 600;
  font-size: 0.94rem;
  transition:
    transform 0.2s ease,
    background 0.2s ease,
    border-color 0.2s ease,
    color 0.2s ease;
}

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

.button-primary {
  color: white;
  background: var(--accent);
  border: 1px solid var(--accent);
}

.button-primary:hover {
  background: var(--accent-hover);
  border-color: var(--accent-hover);
}

.button-secondary {
  color: var(--text-main);
  background: rgba(255, 255, 255, 0.02);
  border: 1px solid var(--border);
}

.button-secondary:hover {
  background: var(--surface-light);
  border-color: rgba(245, 245, 244, 0.24);
}

/* Hero */

.hero {
  min-height: calc(100vh - var(--nav-height));
  display: flex;
  align-items: center;
}

.hero-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(360px, 520px);
  gap: 3rem;
  align-items: center;
}

.eyebrow {
  color: var(--accent-hover);
  font-family: var(--font-mono);
  font-size: 0.82rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  margin-bottom: 0.8rem;
}

.hero h1 {
  max-width: 760px;
  font-size: clamp(2.3rem, 7vw, 5.2rem);
  line-height: 0.98;
  letter-spacing: -0.06em;
  margin-bottom: 1.3rem;
}

.hero-subtitle {
  max-width: 680px;
  color: var(--text-muted);
  font-size: clamp(1rem, 2vw, 1.18rem);
  margin-bottom: 1rem;
}

.author-line {
  color: var(--text-main);
  font-weight: 600;
  margin-bottom: 1.3rem;
}

.metadata-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem 0.85rem;
  color: var(--text-muted);
  font-size: 0.88rem;
  margin-bottom: 1.2rem;
}

.tag-list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
  margin-bottom: 1.8rem;
}

.tag {
  display: inline-flex;
  color: var(--text-muted);
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.35rem 0.7rem;
  font-size: 0.8rem;
  transition: border-color 0.2s ease, color 0.2s ease, background 0.2s ease;
}

.tag:hover {
  color: var(--text-main);
  border-color: rgba(153, 27, 27, 0.7);
  background: var(--accent-soft);
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.8rem;
}

/* Terminal */

.terminal-window {
  border: 1px solid rgba(153, 27, 27, 0.32);
  background: var(--code-bg);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow);
  transform: translateY(0);
  animation: terminalFloat 7s ease-in-out infinite;
}

@keyframes terminalFloat {
  0%,
  100% {
    transform: translateY(0);
  }

  50% {
    transform: translateY(-10px);
  }
}

.terminal-header {
  height: 48px;
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 0 1rem;
  background: #111318;
  border-bottom: 1px solid var(--border);
}

.terminal-dots {
  display: flex;
  gap: 0.45rem;
}

.dot {
  width: 12px;
  height: 12px;
  border-radius: 999px;
}

.dot-red {
  background: #ff5f57;
}

.dot-yellow {
  background: #ffbd2e;
}

.dot-green {
  background: #28c840;
}

.terminal-title {
  color: var(--text-muted);
  font-family: var(--font-mono);
  font-size: 0.82rem;
}

.terminal-body {
  min-height: 350px;
  padding: 1.2rem;
  font-family: var(--font-mono);
  font-size: 0.86rem;
  overflow: hidden;
}

.terminal-line {
  margin-bottom: 0.65rem;
  opacity: 0;
  transform: translateY(6px);
  animation: revealLine 0.45s ease forwards;
}

@keyframes revealLine {
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.terminal-prompt {
  color: var(--terminal-green);
  margin-right: 0.45rem;
}

.terminal-command {
  color: var(--code-text);
}

.terminal-output {
  color: var(--text-muted);
  white-space: pre-line;
  margin-bottom: 0.85rem;
}

.cursor {
  display: inline-block;
  width: 8px;
  height: 1.1em;
  background: var(--code-text);
  vertical-align: -0.15em;
  animation: blink 1s step-end infinite;
}

@keyframes blink {
  50% {
    opacity: 0;
  }
}

/* Note / Intro */

.ethical-note {
  border: 1px solid rgba(153, 27, 27, 0.42);
  border-left: 4px solid var(--accent);
  background: var(--accent-soft);
  border-radius: var(--radius-md);
  padding: 1.3rem;
}

.note-label {
  color: var(--accent-hover);
  font-family: var(--font-mono);
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  margin-bottom: 0.45rem;
}

.intro-section h2,
.article-header h2,
.about-card h2 {
  font-size: clamp(1.7rem, 4vw, 2.6rem);
  line-height: 1.08;
  letter-spacing: -0.04em;
  margin-bottom: 1rem;
}

.intro-section p,
.article-header p,
.about-card p {
  color: var(--text-muted);
  margin-bottom: 1rem;
}

/* Levels Layout */

.levels-layout {
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
  gap: 2.2rem;
  align-items: start;
}

.levels-sidebar {
  position: sticky;
  top: calc(var(--nav-height) + 1.5rem);
}

.sidebar-card {
  max-height: calc(100vh - var(--nav-height) - 3rem);
  overflow: auto;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  background: rgba(18, 21, 27, 0.82);
  padding: 1.1rem;
}

.toc-title {
  color: var(--text-main);
  font-weight: 700;
  font-size: 0.9rem;
  margin-bottom: 0.85rem;
}

.toc-list {
  list-style: none;
}

.toc-list li + li {
  margin-top: 0.3rem;
}

.toc-link {
  display: block;
  color: var(--text-muted);
  border-left: 2px solid transparent;
  padding: 0.35rem 0 0.35rem 0.8rem;
  font-size: 0.9rem;
  transition: all 0.2s ease;
}

.toc-link:hover {
  color: var(--text-main);
}

.toc-link.active {
  color: var(--accent-hover);
  border-left-color: var(--accent-hover);
  background: linear-gradient(90deg, var(--accent-soft), transparent);
}

.mobile-toc {
  display: none;
  margin-bottom: 1.2rem;
}

.mobile-toc-button {
  width: 100%;
  min-height: 48px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-main);
  border-radius: var(--radius-md);
  padding: 0 1rem;
  font-weight: 700;
}

.mobile-toc-panel {
  display: none;
  border: 1px solid var(--border);
  border-top: 0;
  border-radius: 0 0 var(--radius-md) var(--radius-md);
  background: var(--surface);
  padding: 1rem;
}

.mobile-toc-panel.open {
  display: block;
}

.article-header {
  border-bottom: 1px solid var(--border);
  padding-bottom: 1.5rem;
  margin-bottom: 1.5rem;
}

/* Level Cards */

.level-card {
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  background: rgba(18, 21, 27, 0.92);
  overflow: hidden;
  margin-bottom: 1rem;
  transition: border-color 0.2s ease, transform 0.2s ease;
}

.level-card:hover {
  border-color: rgba(153, 27, 27, 0.5);
}

.level-header {
  width: 100%;
  border: 0;
  background: transparent;
  color: var(--text-main);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1.15rem;
  text-align: left;
}

.level-title-group {
  display: grid;
  gap: 0.35rem;
}

.level-title {
  font-size: 1.05rem;
  font-weight: 700;
}

.status-badge {
  width: fit-content;
  border-radius: 999px;
  padding: 0.2rem 0.55rem;
  font-size: 0.72rem;
  font-family: var(--font-mono);
}

.status-completed {
  color: var(--terminal-green);
  background: rgba(34, 197, 94, 0.12);
  border: 1px solid rgba(34, 197, 94, 0.22);
}

.status-learning {
  color: var(--terminal-yellow);
  background: rgba(250, 204, 21, 0.11);
  border: 1px solid rgba(250, 204, 21, 0.22);
}

.accordion-icon {
  color: var(--text-muted);
  transition: transform 0.2s ease;
}

.level-card.open .accordion-icon {
  transform: rotate(180deg);
}

.level-panel {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s ease;
}

.level-inner {
  border-top: 1px solid var(--border);
  padding: 1.2rem;
  background: rgba(11, 13, 16, 0.6);
}

.content-block + .content-block {
  margin-top: 1.25rem;
}

.content-label {
  color: var(--accent-hover);
  font-family: var(--font-mono);
  font-size: 0.78rem;
  text-transform: uppercase;
  font-weight: 700;
  letter-spacing: 0.02em;
  margin-bottom: 0.45rem;
}

.level-text {
  color: var(--text-muted);
}

/* Code Blocks */

.code-wrapper {
  position: relative;
  border: 1px solid rgba(153, 27, 27, 0.38);
  background: var(--code-bg);
  border-radius: var(--radius-sm);
  overflow: hidden;
}

.code-block {
  display: block;
  color: var(--terminal-green);
  font-family: var(--font-mono);
  font-size: 0.88rem;
  white-space: pre-wrap;
  overflow-x: auto;
  padding: 1rem;
  padding-right: 5rem;
}

.copy-button {
  position: absolute;
  top: 0.55rem;
  right: 0.55rem;
  border: 1px solid var(--border);
  background: var(--surface-light);
  color: var(--text-muted);
  border-radius: 999px;
  padding: 0.28rem 0.6rem;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  transition: all 0.2s ease;
}

.copy-button:hover {
  color: white;
  border-color: var(--accent);
  background: var(--accent);
}

/* Closing / About / Footer */

.closing-note {
  margin-top: 2rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  background: rgba(255, 255, 255, 0.02);
  padding: 1.2rem;
  color: var(--text-muted);
}

.closing-note p + p {
  margin-top: 0.65rem;
}

.about-card {
  border: 1px solid var(--border);
  background:
    linear-gradient(135deg, rgba(153, 27, 27, 0.12), transparent),
    var(--surface);
  border-radius: var(--radius-lg);
  padding: clamp(1.4rem, 4vw, 2.5rem);
  text-align: center;
  box-shadow: var(--shadow);
}

.about-card .button {
  margin-top: 0.6rem;
}

.site-footer {
  border-top: 1px solid var(--border);
  background: rgba(18, 21, 27, 0.9);
  padding: 2rem 0;
}

.footer-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.5rem;
}

.footer-text {
  color: var(--text-muted);
  font-size: 0.9rem;
}

/* Back to Top */

.back-to-top {
  position: fixed;
  right: 1.2rem;
  bottom: 1.2rem;
  z-index: 800;
  border: 1px solid rgba(153, 27, 27, 0.5);
  background: var(--accent);
  color: white;
  border-radius: 999px;
  min-height: 42px;
  padding: 0 0.9rem;
  font-weight: 700;
  opacity: 0;
  pointer-events: none;
  transform: translateY(12px);
  transition: all 0.2s ease;
}

.back-to-top.visible {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0);
}

.back-to-top:hover {
  background: var(--accent-hover);
}

/* Responsive */

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

  .terminal-window {
    max-width: 720px;
  }

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

  .levels-sidebar {
    display: none;
  }

  .mobile-toc {
    display: block;
  }
}

@media (max-width: 760px) {
  .mobile-menu-button {
    display: inline-flex;
  }

  .nav-menu {
    position: fixed;
    top: var(--nav-height);
    left: 1rem;
    right: 1rem;
    display: none;
    flex-direction: column;
    align-items: stretch;
    gap: 0.2rem;
    padding: 1rem;
    border: 1px solid var(--border);
    border-radius: var(--radius-md);
    background: rgba(18, 21, 27, 0.98);
    box-shadow: var(--shadow);
  }

  .nav-menu.open {
    display: flex;
  }

  .nav-link,
  .github-link {
    padding: 0.75rem;
    border-radius: var(--radius-sm);
  }

  .nav-link:hover,
  .github-link:hover {
    background: var(--surface-light);
  }

  .language-switcher {
    width: fit-content;
    margin-top: 0.4rem;
  }

  .hero {
    min-height: auto;
    padding-top: 4rem;
  }

  .section-padding {
    padding: 4rem 0;
  }

  .section-padding-small {
    padding: 2.5rem 0;
  }

  .metadata-row {
    gap: 0.35rem 0.7rem;
  }

  .terminal-body {
    min-height: 310px;
    font-size: 0.78rem;
  }

  .footer-inner {
    flex-direction: column;
    text-align: center;
  }
}

@media (max-width: 480px) {
  .page-container {
    width: min(100% - 1rem, 1180px);
  }

  .hero-actions {
    flex-direction: column;
  }

  .button {
    width: 100%;
  }

  .terminal-body {
    padding: 0.9rem;
  }

  .code-block {
    font-size: 0.78rem;
    padding-right: 1rem;
    padding-top: 2.8rem;
  }

  .copy-button {
    left: 0.7rem;
    right: auto;
  }

  .level-header {
    align-items: flex-start;
  }

  .back-to-top {
    right: 0.8rem;
    bottom: 0.8rem;
  }
}