/* ============================================ */
/* CSS RESET & BASE STYLES                      */
/* ============================================ */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  /* Color palette - academic, mathematical */
  --color-bg: #fafaf7;
  --color-bg-elevated: #ffffff;
  --color-bg-dark: #1a1d2e;
  --color-ink: #1c1f2e;
  --color-ink-muted: #4a4f66;
  --color-ink-faint: #7a809a;
  --color-border: #e4e2dc;
  --color-border-strong: #c8c5b8;

  /* Accent colors */
  --color-accent: #6b4ea8; /* deep violet - mathematical */
  --color-accent-hover: #553d8a;
  --color-accent-light: #ede8f7;
  --color-gold: #b8893a; /* algebraic/optimal highlight */
  --color-gold-light: #f7efd9;
  --color-rust: #b85c3a; /* transcendental/expensive */
  --color-teal: #2d7a7a; /* framework accent */

  /* Typography */
  --font-serif: 'Iowan Old Style', 'Palatino Linotype', Palatino, 'URW Palladio L', Georgia, serif;
  --font-sans: -apple-system, BlinkMacSystemFont, 'Inter', 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'SF Mono', Menlo, Consolas, 'Courier New', monospace;

  /* Spacing */
  --space-xs: 0.5rem;
  --space-sm: 1rem;
  --space-md: 1.5rem;
  --space-lg: 2.5rem;
  --space-xl: 4rem;
  --space-2xl: 6rem;

  /* Layout */
  --content-width: 720px;
  --content-width-wide: 980px;

  /* Effects */
  --shadow-sm: 0 1px 2px rgba(28, 31, 46, 0.05);
  --shadow-md: 0 4px 16px rgba(28, 31, 46, 0.08);
  --shadow-lg: 0 12px 40px rgba(28, 31, 46, 0.12);
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --transition: 200ms ease;
}

html {
  scroll-behavior: smooth;
  font-size: 17px;
}

body.article-page {
  font-family: var(--font-serif);
  line-height: 1.7;
  color: var(--color-ink);
  background: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* ============================================ */
/* HEADER / NAVIGATION                          */
/* ============================================ */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(250, 250, 247, 0.92);
  backdrop-filter: saturate(180%) blur(12px);
  -webkit-backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--color-border);
}

.site-nav {
  max-width: var(--content-width-wide);
  margin: 0 auto;
  padding: 0.875rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  font-family: var(--font-sans);
}

.nav-brand .brand-link {
  font-weight: 700;
  font-size: 1rem;
  color: var(--color-ink);
  text-decoration: none;
  letter-spacing: -0.01em;
  border-bottom: 2px solid var(--color-accent);
  padding-bottom: 1px;
}

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

.nav-link {
  display: inline-block;
  padding: 0.4rem 0.75rem;
  font-size: 0.85rem;
  color: var(--color-ink-muted);
  text-decoration: none;
  border-radius: var(--radius-sm);
  transition:
    background var(--transition),
    color var(--transition);
}

.nav-link:hover {
  background: var(--color-accent-light);
  color: var(--color-accent);
}

/* ============================================ */
/* HERO SECTION                                 */
/* ============================================ */
.hero-section {
  background: linear-gradient(180deg, #fafaf7 0%, #f3f1ea 100%);
  padding: var(--space-2xl) 1.5rem var(--space-xl);
  border-bottom: 1px solid var(--color-border);
  position: relative;
  overflow: hidden;
}

.hero-section::before {
  content: 'Σ';
  position: absolute;
  top: -3rem;
  right: -2rem;
  font-size: 28rem;
  font-family: var(--font-serif);
  color: rgba(107, 78, 168, 0.04);
  line-height: 1;
  pointer-events: none;
  user-select: none;
}

.hero-content {
  max-width: var(--content-width);
  margin: 0 auto;
  position: relative;
  z-index: 1;
}

.article-eyebrow {
  font-family: var(--font-sans);
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--color-accent);
  margin-bottom: var(--space-md);
}

.article-title {
  font-size: clamp(2.25rem, 5vw, 3.75rem);
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.02em;
  color: var(--color-ink);
  margin-bottom: var(--space-sm);
}

.article-subtitle {
  font-size: clamp(1.1rem, 2.2vw, 1.4rem);
  font-style: italic;
  color: var(--color-ink-muted);
  font-weight: 400;
  margin-bottom: var(--space-lg);
  line-height: 1.4;
}

.article-meta {
  font-family: var(--font-sans);
  font-size: 0.85rem;
  color: var(--color-ink-faint);
  display: flex;
  gap: 0.5rem;
  align-items: center;
  flex-wrap: wrap;
}

.meta-separator {
  color: var(--color-border-strong);
}

/* ============================================ */
/* MAIN ARTICLE                                 */
/* ============================================ */
.article-main {
  max-width: var(--content-width);
  margin: 0 auto;
  padding: var(--space-xl) 1.5rem;
}

.article-section {
  margin-bottom: var(--space-2xl);
  scroll-margin-top: 5rem;
}

.section-heading {
  font-size: clamp(1.6rem, 3.2vw, 2.1rem);
  font-weight: 700;
  line-height: 1.25;
  letter-spacing: -0.015em;
  color: var(--color-ink);
  margin-bottom: var(--space-lg);
  padding-bottom: var(--space-sm);
  border-bottom: 2px solid var(--color-border);
  position: relative;
}

.section-heading::before {
  content: '';
  position: absolute;
  bottom: -2px;
  left: 0;
  width: 3.5rem;
  height: 2px;
  background: var(--color-accent);
}

.subsection {
  margin-top: var(--space-lg);
  margin-bottom: var(--space-lg);
}

.subsection-heading {
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--color-ink);
  margin-bottom: var(--space-md);
  letter-spacing: -0.01em;
}

.section-paragraph {
  margin-bottom: var(--space-md);
  color: var(--color-ink);
  font-size: 1.05rem;
}

.lead-paragraph {
  font-size: 1.18rem;
  line-height: 1.65;
  color: var(--color-ink);
}

.section-paragraph em {
  font-style: italic;
  color: var(--color-accent);
}

.section-paragraph strong {
  font-weight: 700;
}

/* ============================================ */
/* MATH BLOCKS                                  */
/* ============================================ */
.math-block {
  background: var(--color-bg-dark);
  color: #f3f1ea;
  padding: 1.1rem 1.4rem;
  border-radius: var(--radius-md);
  overflow-x: auto;
  margin: var(--space-md) 0;
  border-left: 3px solid var(--color-accent);
  box-shadow: var(--shadow-sm);
}

.math-code {
  font-family: var(--font-mono);
  font-size: 0.95rem;
  line-height: 1.6;
  color: #f3f1ea;
  white-space: pre;
}

.highlight-math {
  border-left-color: var(--color-gold);
  background: linear-gradient(135deg, #1a1d2e 0%, #2b2238 100%);
}

/* ============================================ */
/* LISTS                                        */
/* ============================================ */
.example-list,
.feature-list,
.conclusion-list,
.finding-list {
  list-style: none;
  margin: var(--space-md) 0;
  padding-left: 0;
}

.example-item,
.feature-item,
.conclusion-item,
.finding-item {
  padding: 0.5rem 0 0.5rem 1.5rem;
  position: relative;
  font-size: 1.02rem;
  line-height: 1.6;
}

.example-item::before,
.feature-item::before,
.conclusion-item::before,
.finding-item::before {
  content: '▸';
  position: absolute;
  left: 0;
  color: var(--color-accent);
  font-weight: bold;
}

.example-item {
  font-family: var(--font-mono);
  font-size: 0.95rem;
}

.numbered-list,
.component-list {
  list-style: none;
  counter-reset: item;
  margin: var(--space-md) 0;
  padding-left: 0;
}

.numbered-item,
.component-item {
  counter-increment: item;
  padding: 0.6rem 0 0.6rem 2.5rem;
  position: relative;
  font-size: 1.02rem;
  line-height: 1.6;
}

.numbered-item::before,
.component-item::before {
  content: counter(item);
  position: absolute;
  left: 0;
  top: 0.6rem;
  width: 1.75rem;
  height: 1.75rem;
  background: var(--color-accent);
  color: white;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-sans);
  font-size: 0.8rem;
  font-weight: 700;
}

.component-name {
  color: var(--color-accent);
}

/* Check list */
.check-list {
  list-style: none;
  margin: var(--space-md) 0;
  padding-left: 0;
}

.check-item {
  padding: 0.6rem 0 0.6rem 2rem;
  position: relative;
  font-size: 1.02rem;
  line-height: 1.6;
}

.check-item.check-yes::before {
  content: '✓';
  position: absolute;
  left: 0;
  color: var(--color-teal);
  font-weight: bold;
  font-size: 1.2rem;
}

.check-item.check-no::before {
  content: '✗';
  position: absolute;
  left: 0;
  color: var(--color-rust);
  font-weight: bold;
  font-size: 1.2rem;
}

/* ============================================ */
/* CALLOUTS                                     */
/* ============================================ */
.callout {
  background: var(--color-bg-elevated);
  border-left: 4px solid var(--color-accent);
  padding: var(--space-md) var(--space-md);
  margin: var(--space-lg) 0;
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  box-shadow: var(--shadow-sm);
}

.callout-title {
  font-family: var(--font-sans);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--color-accent);
  margin-bottom: var(--space-sm);
}

.callout-text {
  margin-bottom: var(--space-sm);
  font-size: 1rem;
  color: var(--color-ink);
}

.callout-text:last-child {
  margin-bottom: 0;
}

.callout-caveats {
  background: linear-gradient(135deg, var(--color-accent-light) 0%, #f5f0ff 100%);
  border-left-color: var(--color-accent);
}

.dual-callout {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-md);
  margin: var(--space-lg) 0;
}

@media (min-width: 720px) {
  .dual-callout {
    grid-template-columns: 1fr 1fr;
  }
}

.callout-shown {
  border-left-color: var(--color-teal);
  background: #effaf7;
}

.callout-shown .callout-title {
  color: var(--color-teal);
}

.callout-not-shown {
  border-left-color: var(--color-rust);
  background: #fbf2ee;
}

.callout-not-shown .callout-title {
  color: var(--color-rust);
}

/* ============================================ */
/* BLOCKQUOTES                                  */
/* ============================================ */
.central-claim,
.definition-blockquote {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  line-height: 1.5;
  font-style: italic;
  color: var(--color-ink);
  padding: var(--space-md) var(--space-lg);
  margin: var(--space-lg) 0;
  border-left: 4px solid var(--color-gold);
  background: var(--color-gold-light);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  position: relative;
}

.central-claim::before,
.definition-blockquote::before {
  content: '\201C';
  position: absolute;
  top: -0.5rem;
  left: 0.5rem;
  font-size: 3.5rem;
  color: var(--color-gold);
  font-family: Georgia, serif;
  opacity: 0.3;
  line-height: 1;
}

/* ============================================ */
/* SERIES CARDS                                 */
/* ============================================ */
.series-card {
  background: var(--color-bg-elevated);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-md);
  margin: var(--space-md) 0;
  transition:
    transform var(--transition),
    box-shadow var(--transition);
  border-top: 3px solid var(--color-accent);
}

.series-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.series-card-leibniz {
  border-top-color: var(--color-rust);
}
.series-card-nilakantha {
  border-top-color: var(--color-accent);
}
.series-card-wallis {
  border-top-color: var(--color-teal);
}

.series-name {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--color-ink);
  margin-bottom: 0.25rem;
}

.series-description {
  font-family: var(--font-sans);
  font-size: 0.85rem;
  color: var(--color-ink-faint);
  font-style: italic;
  margin-bottom: var(--space-sm);
}

.series-card .math-block {
  margin: 0;
}

/* ============================================ */
/* RESULT STATEMENTS                            */
/* ============================================ */
.result-statement {
  font-family: var(--font-mono);
  font-size: 1rem;
  background: var(--color-accent-light);
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-sm);
  border-left: 3px solid var(--color-accent);
  margin: var(--space-md) 0;
  color: var(--color-ink);
}

.result-optimal {
  background: var(--color-gold-light);
  border-left-color: var(--color-gold);
  font-weight: 600;
}

/* ============================================ */
/* CLASSIFICATION TABLE                         */
/* ============================================ */
.table-wrapper {
  overflow-x: auto;
  margin: var(--space-md) 0;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
}

.complexity-table {
  width: 100%;
  border-collapse: collapse;
  background: var(--color-bg-elevated);
  font-family: var(--font-sans);
  font-size: 0.95rem;
}

.table-head {
  background: var(--color-bg-dark);
  color: #f3f1ea;
}

.table-header {
  padding: 0.9rem 1rem;
  text-align: left;
  font-weight: 600;
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.table-row {
  border-top: 1px solid var(--color-border);
  transition: background var(--transition);
}

.table-row:hover {
  background: #faf6ee;
}

.table-cell {
  padding: 0.9rem 1rem;
  vertical-align: top;
}

.cell-iteration,
.cell-bitlength {
  font-family: var(--font-mono);
  font-size: 0.9rem;
  color: var(--color-ink-muted);
}

.table-row-highlight {
  background: var(--color-gold-light);
}

.table-row-highlight:hover {
  background: #f3eacd;
}

.table-row-highlight .cell-bitlength {
  color: var(--color-gold);
  font-weight: 600;
}

/* ============================================ */
/* FRAMEWORK GRID                               */
/* ============================================ */
.framework-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-md);
  margin: var(--space-lg) 0;
}

@media (min-width: 720px) {
  .framework-grid {
    grid-template-columns: repeat(3, 1fr);
  }
}

.framework-card {
  background: var(--color-bg-elevated);
  padding: var(--space-md);
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border);
  transition:
    transform var(--transition),
    box-shadow var(--transition);
}

.framework-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
}

.framework-card-classical {
  border-top: 3px solid var(--color-rust);
}
.framework-card-diophantine {
  border-top: 3px solid var(--color-teal);
}
.framework-card-ko-friedman {
  border-top: 3px solid var(--color-accent);
}

.framework-name {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--color-ink);
  margin-bottom: var(--space-sm);
  line-height: 1.3;
}

.framework-description {
  font-size: 0.95rem;
  color: var(--color-ink-muted);
  line-height: 1.6;
}

/* ============================================ */
/* COMPLEXITY CLASS HIERARCHY                   */
/* ============================================ */
.class-hierarchy {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-md);
  margin: var(--space-lg) 0;
}

.complexity-class {
  background: var(--color-bg-elevated);
  padding: var(--space-md) var(--space-md) var(--space-md) 5rem;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
  position: relative;
  border: 1px solid var(--color-border);
  overflow: hidden;
}

.class-label {
  position: absolute;
  top: 0;
  left: 0;
  width: 4rem;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-sans);
  font-size: 1.4rem;
  font-weight: 700;
  color: white;
}

.class-rc1 {
  border-left: 4px solid var(--color-gold);
}
.class-rc1 .class-label {
  background: var(--color-gold);
}

.class-rc2 {
  border-left: 4px solid var(--color-accent);
}
.class-rc2 .class-label {
  background: var(--color-accent);
}

.class-rc3 {
  border-left: 4px solid var(--color-rust);
}
.class-rc3 .class-label {
  background: var(--color-rust);
}

.class-name {
  font-size: 1.05rem;
  font-weight: 700;
  margin-bottom: 0.25rem;
  color: var(--color-ink);
}

.class-formula {
  font-family: var(--font-mono);
  font-size: 0.9rem;
  color: var(--color-ink-muted);
  background: var(--color-bg);
  padding: 0.4rem 0.7rem;
  border-radius: var(--radius-sm);
  display: inline-block;
  margin-bottom: var(--space-sm);
}

.class-examples {
  font-size: 0.95rem;
  color: var(--color-ink-muted);
  line-height: 1.5;
}

/* ============================================ */
/* SPECIAL PARAGRAPHS                           */
/* ============================================ */
.closing-paragraph {
  font-size: 1.15rem;
  font-style: italic;
  color: var(--color-ink-muted);
  border-top: 1px solid var(--color-border);
  padding-top: var(--space-md);
  margin-top: var(--space-lg);
}

.subsection-optimal .result-statement {
  background: linear-gradient(135deg, var(--color-gold-light), #fff8e2);
  border-left-width: 4px;
}

/* ============================================ */
/* FOOTER                                       */
/* ============================================ */
.site-footer {
  background: var(--color-bg-dark);
  color: #c8c5b8;
  padding: var(--space-xl) 1.5rem var(--space-md);
  margin-top: var(--space-2xl);
}

.footer-content {
  max-width: var(--content-width-wide);
  margin: 0 auto;
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-lg);
  padding-bottom: var(--space-lg);
  border-bottom: 1px solid rgba(255, 255, 255, 0.08);
}

@media (min-width: 720px) {
  .footer-content {
    grid-template-columns: 2fr 1fr 1fr;
  }
}

.footer-heading {
  font-family: var(--font-sans);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: #f3f1ea;
  margin-bottom: var(--space-sm);
}

.footer-text {
  font-size: 0.95rem;
  line-height: 1.6;
  color: #a8a59a;
}

.footer-tag-list {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
}

.footer-tag {
  font-family: var(--font-sans);
  font-size: 0.78rem;
  padding: 0.3rem 0.7rem;
  background: rgba(255, 255, 255, 0.06);
  border: 1px solid rgba(255, 255, 255, 0.1);
  border-radius: 999px;
  color: #c8c5b8;
}

.footer-bottom {
  max-width: var(--content-width-wide);
  margin: 0 auto;
  padding-top: var(--space-md);
  text-align: center;
}

.footer-copyright {
  font-family: var(--font-sans);
  font-size: 0.8rem;
  color: #6a6e7c;
}

/* ============================================ */
/* RESPONSIVE ADJUSTMENTS                       */
/* ============================================ */
@media (max-width: 640px) {
  html {
    font-size: 16px;
  }

  .nav-menu {
    gap: 0;
  }

  .nav-link {
    padding: 0.4rem 0.5rem;
    font-size: 0.78rem;
  }

  .hero-section {
    padding: var(--space-xl) 1.25rem var(--space-lg);
  }

  .article-main {
    padding: var(--space-lg) 1.25rem;
  }

  .article-section {
    margin-bottom: var(--space-xl);
  }

  .math-block {
    padding: 0.9rem 1rem;
  }

  .math-code {
    font-size: 0.85rem;
  }

  .complexity-class {
    padding-left: 4rem;
  }

  .class-label {
    width: 3rem;
    font-size: 1.1rem;
  }
}

@media (max-width: 480px) {
  .nav-brand .brand-link {
    font-size: 0.9rem;
  }

  .article-title {
    font-size: 2rem;
  }
}

/* ============================================ */
/* SELECTION & FOCUS                            */
/* ============================================ */
::selection {
  background: var(--color-accent);
  color: white;
}

a:focus-visible,
button:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}