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

:root {
  --bg: #0a0c10;
  --bg-elevated: #0f1117;
  --bg-card: #151820;
  --bg-card-hover: #1a1f2e;
  --border: #1e2235;
  --border-hover: #3d4060;
  --text-primary: #f0f2f7;
  --text-secondary: #9399b0;
  --text-muted: #5d6275;
  --accent: #6366f1;
  --accent-glow: rgba(99, 102, 241, 0.15);
  --accent-soft: #1e1b4b;

  --cat-dev: #60a5fa;
  --cat-dev-bg: rgba(96, 165, 250, 0.1);
  --cat-service: #34d399;
  --cat-service-bg: rgba(52, 211, 153, 0.1);
  --cat-legal: #fbbf24;
  --cat-legal-bg: rgba(251, 191, 36, 0.1);
  --cat-research: #a78bfa;
  --cat-research-bg: rgba(167, 139, 250, 0.1);
  --cat-content: #f472b6;
  --cat-content-bg: rgba(244, 114, 182, 0.1);
  --cat-finance: #22d3ee;
  --cat-finance-bg: rgba(34, 211, 238, 0.1);
  --cat-productivity: #a3e635;
  --cat-productivity-bg: rgba(163, 230, 53, 0.1);
  --cat-ops: #fb923c;
  --cat-ops-bg: rgba(251, 146, 60, 0.1);
  --cat-education: #e879f9;
  --cat-education-bg: rgba(232, 121, 249, 0.1);

  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 20px;

  --shadow-card: 0 2px 8px rgba(0,0,0,0.3), 0 1px 2px rgba(0,0,0,0.2);
  --shadow-card-hover: 0 12px 40px rgba(0,0,0,0.4), 0 4px 12px rgba(0,0,0,0.3);

  --transition-fast: 0.15s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-medium: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

html {
  scroll-behavior: smooth;
}

body {
  background: var(--bg);
  color: var(--text-primary);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  line-height: 1.7;
  font-size: 15px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

.container {
  max-width: 1240px;
  margin: 0 auto;
  padding: 0 28px;
}

/* ========== Nav ========== */
.top-nav {
  position: sticky;
  top: 0;
  z-index: 200;
  background: rgba(10, 12, 16, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  padding: 0;
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 48px;
}

.nav-logo {
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text-secondary);
  letter-spacing: -0.01em;
}

.nav-links {
  display: flex;
  gap: 4px;
}

.nav-link {
  font-size: 0.82rem;
  color: var(--text-muted);
  text-decoration: none;
  padding: 6px 14px;
  border-radius: 8px;
  transition: all var(--transition-fast);
}

.nav-link:hover {
  color: var(--text-primary);
  background: rgba(255,255,255,0.05);
}

.nav-link.active {
  color: var(--text-primary);
  background: rgba(99, 102, 241, 0.12);
}

/* ========== Header ========== */
header {
  padding: 80px 0 56px;
  border-bottom: 1px solid var(--border);
  background: linear-gradient(180deg, var(--bg) 0%, var(--bg-elevated) 100%);
  position: relative;
  overflow: hidden;
}

header::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -20%;
  width: 60%;
  height: 200%;
  background: radial-gradient(ellipse, rgba(99, 102, 241, 0.05) 0%, transparent 60%);
  pointer-events: none;
}

header::after {
  content: '';
  position: absolute;
  top: -30%;
  right: -10%;
  width: 40%;
  height: 150%;
  background: radial-gradient(ellipse, rgba(34, 211, 238, 0.03) 0%, transparent 60%);
  pointer-events: none;
}

.header-inner {
  max-width: 1240px;
  margin: 0 auto;
  padding: 0 28px;
  position: relative;
  z-index: 1;
}

header h1 {
  font-size: 3rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  color: var(--text-primary);
  margin-bottom: 14px;
  background: linear-gradient(135deg, var(--text-primary) 0%, #c4c9e0 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.subtitle {
  font-size: 1.15rem;
  color: var(--text-secondary);
  max-width: 580px;
  line-height: 1.7;
}


/* ========== Intro ========== */
.intro {
  padding: 56px 0;
  border-bottom: 1px solid var(--border);
}

.intro-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
}

.intro-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px;
  transition: transform var(--transition-medium), border-color var(--transition-medium), box-shadow var(--transition-medium);
}

.intro-card:hover {
  transform: translateY(-2px);
  border-color: var(--border-hover);
  box-shadow: var(--shadow-card);
}

.ref-list li {
  opacity: 0;
  transform: translateY(12px);
  transition: opacity 0.4s ease, transform 0.4s ease;
}

.ref-list li.revealed {
  opacity: 1;
  transform: translateY(0);
}

.intro-icon {
  font-size: 1.6rem;
  display: block;
  margin-bottom: 14px;
}

.intro-card h3 {
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: 10px;
  color: var(--text-primary);
}

.intro-card p {
  font-size: 0.88rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

.intro-card strong {
  color: var(--text-primary);
}

/* ========== Cases Section ========== */
.cases-section {
  padding: 64px 0;
}

.section-header {
  margin-bottom: 36px;
}

.section-header h2 {
  font-size: 1.75rem;
  font-weight: 700;
  margin-bottom: 20px;
  color: var(--text-primary);
}

/* Search */
.search-container {
  position: relative;
  margin-bottom: 20px;
}

.search-input {
  width: 100%;
  padding: 12px 16px 12px 44px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: 0.9rem;
  font-family: inherit;
  outline: none;
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.search-input::placeholder {
  color: var(--text-muted);
}

.search-input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.search-icon {
  position: absolute;
  left: 14px;
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-muted);
  width: 18px;
  height: 18px;
  pointer-events: none;
}

/* Filters */
.filters {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
}

.filter-btn {
  background: var(--bg-card);
  border: 1px solid var(--border);
  color: var(--text-secondary);
  padding: 7px 16px;
  border-radius: 20px;
  font-size: 0.82rem;
  cursor: pointer;
  transition: all var(--transition-fast);
  font-family: inherit;
  white-space: nowrap;
}

.filter-btn:hover {
  border-color: var(--border-hover);
  color: var(--text-primary);
  background: var(--bg-card-hover);
}

.filter-btn.active {
  background: var(--accent-soft);
  border-color: var(--accent);
  color: #a5b4fc;
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.filter-count {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 20px;
  height: 20px;
  padding: 0 6px;
  margin-left: 6px;
  background: rgba(255,255,255,0.08);
  border-radius: 10px;
  font-size: 0.7rem;
  font-weight: 600;
}

.results-count {
  font-size: 0.82rem;
  color: var(--text-muted);
  margin-bottom: 20px;
  min-height: 1.4em;
  transition: opacity var(--transition-fast);
}

/* Cases Grid */
.cases-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 22px;
}

.case-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 26px;
  transition: transform var(--transition-medium), border-color var(--transition-medium), box-shadow var(--transition-medium), opacity var(--transition-medium);
  display: flex;
  flex-direction: column;
  gap: 16px;
  position: relative;
  overflow: hidden;
}

.case-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: linear-gradient(90deg, transparent, var(--accent), transparent);
  opacity: 0;
  transition: opacity var(--transition-medium);
}

.case-card:hover {
  border-color: var(--border-hover);
  background: var(--bg-card-hover);
  transform: translateY(-3px);
  box-shadow: var(--shadow-card-hover);
}

.case-card:hover::before {
  opacity: 1;
}

.case-card.hidden {
  display: none;
}

/* Scroll reveal animation */
.case-card {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.5s cubic-bezier(0.25, 0.46, 0.45, 0.94),
              transform 0.5s cubic-bezier(0.25, 0.46, 0.45, 0.94),
              border-color var(--transition-medium),
              box-shadow var(--transition-medium),
              background var(--transition-medium);
}

.case-card.revealed {
  opacity: 1;
  transform: translateY(0);
}

.case-card.revealed:hover {
  transform: translateY(-3px);
}

/* No motion preference */
@media (prefers-reduced-motion: reduce) {
  .case-card {
    opacity: 1;
    transform: none;
    transition: border-color var(--transition-medium), box-shadow var(--transition-medium), background var(--transition-medium);
  }
}

.case-header {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.category-tag {
  font-size: 0.73rem;
  font-weight: 600;
  padding: 4px 11px;
  border-radius: 20px;
  letter-spacing: 0.02em;
}

.category-tag.dev       { background: var(--cat-dev-bg);          color: var(--cat-dev); }
.category-tag.service   { background: var(--cat-service-bg);      color: var(--cat-service); }
.category-tag.legal     { background: var(--cat-legal-bg);        color: var(--cat-legal); }
.category-tag.research  { background: var(--cat-research-bg);     color: var(--cat-research); }
.category-tag.content   { background: var(--cat-content-bg);      color: var(--cat-content); }
.category-tag.finance   { background: var(--cat-finance-bg);      color: var(--cat-finance); }
.category-tag.productivity { background: var(--cat-productivity-bg); color: var(--cat-productivity); }
.category-tag.ops       { background: var(--cat-ops-bg);          color: var(--cat-ops); }
.category-tag.education { background: var(--cat-education-bg);    color: var(--cat-education); }

.new-badge {
  font-size: 0.62rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  color: #0a0c10;
  background: linear-gradient(135deg, #34d399, #6ee7b7);
  padding: 2px 7px;
  border-radius: 4px;
  text-transform: uppercase;
  line-height: 1;
}

.level {
  font-size: 0.72rem;
  color: var(--text-muted);
  margin-left: auto;
  padding: 2px 8px;
  border-radius: 4px;
  background: rgba(255,255,255,0.03);
}

.level-low   { color: #6bcf7f; }
.level-mid   { color: #f5c842; }
.level-high  { color: #f07060; }

.case-card h3 {
  font-size: 1.02rem;
  font-weight: 600;
  line-height: 1.5;
  color: var(--text-primary);
}

.case-meta {
  display: flex;
  gap: 10px;
  align-items: center;
}

.org {
  font-size: 0.78rem;
  color: var(--text-muted);
  background: rgba(255,255,255,0.04);
  padding: 3px 10px;
  border-radius: 6px;
  border: 1px solid var(--border);
}

.case-date {
  font-size: 0.72rem;
  color: var(--text-muted);
  font-family: "SF Mono", "Fira Code", monospace;
  letter-spacing: 0.04em;
  margin-left: auto;
}

/* Before/After */
.case-body {
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.before-after {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}

.before, .after {
  border-radius: var(--radius-sm);
  padding: 14px 16px;
}

.before {
  background: rgba(239, 68, 68, 0.05);
  border: 1px solid rgba(239, 68, 68, 0.12);
}

.after {
  background: rgba(99, 102, 241, 0.06);
  border: 1px solid rgba(99, 102, 241, 0.15);
}

.before label, .after label {
  display: block;
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-bottom: 8px;
}

.before label { color: #f87171; }
.after label  { color: #818cf8; }

.before p, .after p {
  font-size: 0.84rem;
  color: var(--text-secondary);
  line-height: 1.65;
}

.before p strong, .after p strong {
  color: var(--text-primary);
  font-weight: 600;
}

/* Tools Used */
.tools-used {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.tool-tag {
  font-size: 0.7rem;
  background: rgba(255,255,255,0.04);
  border: 1px solid var(--border);
  color: var(--text-muted);
  padding: 3px 10px;
  border-radius: 6px;
  transition: color var(--transition-fast), border-color var(--transition-fast);
}

.case-card:hover .tool-tag {
  border-color: var(--border-hover);
  color: var(--text-secondary);
}

/* Insight */
.case-insight {
  font-size: 0.83rem;
  color: var(--text-secondary);
  background: rgba(99, 102, 241, 0.04);
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent);
  padding: 12px 16px;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  line-height: 1.65;
  margin-top: auto;
}

/* ========== References ========== */
.references-section {
  padding: 64px 0;
  border-top: 1px solid var(--border);
  background: linear-gradient(180deg, transparent 0%, rgba(99, 102, 241, 0.02) 100%);
}

.references-section h2 {
  font-size: 1.75rem;
  font-weight: 700;
  margin-bottom: 10px;
}

.section-desc {
  color: var(--text-secondary);
  margin-bottom: 40px;
  font-size: 0.95rem;
}

.refs-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 28px;
}

.ref-group h3 {
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: 18px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
}

.ref-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 22px;
}

.ref-list li {
  transition: transform var(--transition-fast);
}

.ref-list li:hover {
  transform: translateX(4px);
}

.ref-list li strong {
  display: block;
  font-size: 0.95rem;
  color: var(--text-primary);
  margin-bottom: 3px;
}

.ref-list li span {
  display: block;
  font-size: 0.75rem;
  color: var(--accent);
  margin-bottom: 6px;
  font-family: "SF Mono", "Fira Code", monospace;
}

.ref-link {
  display: block;
  font-size: 0.75rem;
  color: var(--accent);
  margin-bottom: 6px;
  font-family: "SF Mono", "Fira Code", monospace;
  text-decoration: none;
  transition: color var(--transition-fast);
}

.ref-link:hover {
  color: #a5b4fc;
  text-decoration: underline;
}

.ref-link-plain {
  display: block;
  font-size: 0.75rem;
  color: var(--text-muted);
  margin-bottom: 6px;
  font-family: "SF Mono", "Fira Code", monospace;
}

.ref-list li p {
  font-size: 0.82rem;
  color: var(--text-secondary);
  line-height: 1.65;
}

/* ========== Footer ========== */
footer {
  padding: 48px 0;
  border-top: 1px solid var(--border);
  text-align: center;
}

footer p {
  color: var(--text-muted);
  font-size: 0.88rem;
}

.footer-note {
  margin-top: 8px;
  font-size: 0.8rem !important;
  font-style: italic;
}

/* ========== Back to Top ========== */
.back-to-top {
  position: fixed;
  bottom: 28px;
  right: 28px;
  width: 44px;
  height: 44px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-secondary);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(10px);
  transition: all var(--transition-medium);
  z-index: 100;
  box-shadow: var(--shadow-card);
}

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

.back-to-top:hover {
  background: var(--accent-soft);
  border-color: var(--accent);
  color: var(--accent);
  transform: translateY(-2px);
}

.back-to-top svg {
  width: 18px;
  height: 18px;
}

/* ========== Empty State ========== */
.empty-state {
  grid-column: 1 / -1;
  text-align: center;
  padding: 64px 0;
  color: var(--text-muted);
}

.empty-state-icon {
  font-size: 2.5rem;
  margin-bottom: 16px;
  opacity: 0.5;
}

.empty-state-text {
  font-size: 1rem;
  margin-bottom: 8px;
}

.empty-state-hint {
  font-size: 0.85rem;
  color: var(--text-muted);
}

/* ========== Responsive ========== */
@media (max-width: 1024px) {
  .cases-grid { grid-template-columns: 1fr; }
  .refs-grid { grid-template-columns: repeat(2, 1fr); }
  header h1 { font-size: 2.4rem; }
}

@media (max-width: 768px) {
  .intro-grid { grid-template-columns: 1fr; }
  .refs-grid { grid-template-columns: 1fr; }
  .before-after { grid-template-columns: 1fr; }
  .stats-bar { gap: 20px; flex-wrap: wrap; }
  header { padding: 56px 0 40px; }
  header h1 { font-size: 2rem; }
  .container { padding: 0 20px; }
  .case-card { padding: 22px; }
}

@media (max-width: 480px) {
  header h1 { font-size: 1.7rem; }
  .subtitle { font-size: 1rem; }
  .filters { gap: 6px; }
  .filter-btn { padding: 6px 12px; font-size: 0.78rem; }
  .stat-number { font-size: 1.3rem; }
}

/* ========== Scroll Progress ========== */
.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--accent), #22d3ee);
  z-index: 9999;
  transition: width 0.1s linear;
}