@import url('https://fonts.googleapis.com/css2?family=Noto+Sans+KR:wght@300;400;500;700;900&family=Inter:wght@300;400;500;600;700;800;900&display=swap');

:root {
  --bg: #faf9fe;
  --bg-white: #ffffff;
  --bg-warm: #f5f3ff;
  --bg-glass: rgba(255,255,255,0.72);
  --bg-glass-strong: rgba(255,255,255,0.88);
  --text: #1a1a2e;
  --text-secondary: #4a4a6a;
  --text-muted: #9090aa;
  --accent: #7c6cf0;
  --accent-light: #a78bfa;
  --accent-dark: #5b4cc4;
  --accent-pink: #ec4899;
  --accent-orange: #f97316;
  --accent-green: #10b981;
  --gradient-main: linear-gradient(135deg, #7c6cf0 0%, #a78bfa 40%, #c084fc 70%, #ec4899 100%);
  --gradient-warm: linear-gradient(135deg, #7c6cf0 0%, #a78bfa 50%, #f97316 100%);
  --gradient-soft: linear-gradient(180deg, #f5f3ff 0%, #faf9fe 100%);
  --gradient-card: linear-gradient(135deg, rgba(124,108,240,0.05) 0%, rgba(236,72,153,0.03) 100%);
  --gradient-cover: linear-gradient(-45deg, #7c6cf0, #a78bfa, #c084fc, #ec4899, #f97316, #7c6cf0);
  --border: rgba(124,108,240,0.12);
  --border-light: rgba(124,108,240,0.06);
  --radius: 20px;
  --radius-sm: 12px;
  --radius-xs: 8px;
  --shadow-sm: 0 2px 8px rgba(124,108,240,0.06);
  --shadow: 0 4px 20px rgba(124,108,240,0.08);
  --shadow-lg: 0 12px 40px rgba(124,108,240,0.12);
  --shadow-glow: 0 0 30px rgba(124,108,240,0.15);
  --shadow-card-hover: 0 16px 48px rgba(124,108,240,0.16);
  --max-width: 780px;
  --font: 'Noto Sans KR', 'Inter', -apple-system, sans-serif;
  --font-en: 'Inter', -apple-system, sans-serif;
  --transition: cubic-bezier(0.4, 0, 0.2, 1);
}

*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

body::before {
  content: '';
  position: fixed;
  top: 0; left: 0; width: 100%; height: 100%;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 256 256' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)' opacity='0.012'/%3E%3C/svg%3E");
  pointer-events: none;
  z-index: 0;
}
body > * { position: relative; z-index: 1; }

@keyframes gradientShift {
  0% { background-position: 0% 50%; }
  50% { background-position: 100% 50%; }
  100% { background-position: 0% 50%; }
}
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(30px); }
  to { opacity: 1; transform: translateY(0); }
}
@keyframes float {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-8px); }
}
@keyframes floatSlow {
  0%, 100% { transform: translateY(0) rotate(0deg); }
  33% { transform: translateY(-6px) rotate(1deg); }
  66% { transform: translateY(-3px) rotate(-1deg); }
}
@keyframes pulse-glow {
  0%, 100% { box-shadow: 0 0 20px rgba(124,108,240,0.12); }
  50% { box-shadow: 0 0 40px rgba(124,108,240,0.22); }
}
@keyframes bounce-subtle {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-4px); }
}
@keyframes wiggle {
  0%, 100% { transform: rotate(0deg); }
  25% { transform: rotate(-3deg); }
  75% { transform: rotate(3deg); }
}
@keyframes sparkle {
  0%, 100% { opacity: 1; transform: scale(1); }
  50% { opacity: 0.6; transform: scale(1.15); }
}

.scroll-progress {
  position: fixed;
  top: 0; left: 0;
  height: 3px;
  width: 0%;
  background: var(--gradient-main);
  z-index: 300;
  transition: width 0.15s linear;
  box-shadow: 0 0 8px rgba(124,108,240,0.4);
}

.letter-header {
  position: sticky;
  top: 0; z-index: 100;
  background: rgba(250,249,254,0.82);
  backdrop-filter: blur(24px) saturate(180%);
  -webkit-backdrop-filter: blur(24px) saturate(180%);
  border-bottom: 1px solid var(--border-light);
  padding: 0.65rem 0;
  transition: all 0.3s var(--transition);
}
.letter-header.scrolled {
  background: rgba(250,249,254,0.95);
  box-shadow: 0 2px 20px rgba(124,108,240,0.06);
}
.header-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 2rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.header-brand { display: flex; align-items: center; gap: 0.6rem; }
.udemy-logo { height: 24px; opacity: 0.85; transition: opacity 0.2s; }
.udemy-logo:hover { opacity: 1; }
.header-divider { color: var(--border); font-size: 1.1rem; }
.header-title {
  font-family: var(--font-en);
  font-size: 0.95rem;
  font-weight: 700;
  background: var(--gradient-main);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  letter-spacing: -0.02em;
  position: relative;
  top: 1px;
}
.header-actions { display: flex; gap: 0.5rem; align-items: center; }

.lang-toggle {
  display: flex;
  border: 1px solid var(--border);
  border-radius: 20px;
  overflow: hidden;
  background: var(--bg-glass);
  backdrop-filter: blur(8px);
}
.lang-btn {
  padding: 0.35rem 0.7rem;
  border: none;
  background: transparent;
  color: var(--text-muted);
  font-size: 0.72rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.3s var(--transition);
  font-family: var(--font-en);
}
.lang-btn:hover { color: var(--accent); }
.lang-btn.active {
  background: var(--gradient-main);
  color: white;
  border-radius: 18px;
}

.btn-letter {
  padding: 0.45rem 1rem;
  border: 1px solid var(--border);
  background: var(--bg-glass);
  backdrop-filter: blur(8px);
  color: var(--text-secondary);
  border-radius: 25px;
  cursor: pointer;
  font-size: 0.78rem;
  font-weight: 500;
  transition: all 0.3s var(--transition);
  text-decoration: none;
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  white-space: nowrap;
}
.btn-letter:hover {
  border-color: var(--accent);
  color: var(--accent);
  box-shadow: var(--shadow-sm);
  transform: translateY(-1px);
}
.btn-letter.btn-primary {
  background: var(--gradient-main);
  background-size: 200% 200%;
  animation: gradientShift 8s ease infinite;
  color: white;
  border: none;
  font-weight: 600;
}
.btn-letter.btn-primary:hover {
  box-shadow: var(--shadow-glow);
  transform: translateY(-2px);
}

.cover-section {
  background: var(--gradient-cover);
  background-size: 400% 400%;
  animation: gradientShift 15s ease infinite;
  color: white;
  padding: 4.5rem 2rem 5rem;
  text-align: center;
  position: relative;
  overflow: hidden;
  min-height: 520px;
  display: flex;
  align-items: center;
  justify-content: center;
}
.cover-section::before {
  content: '';
  position: absolute;
  top: -50%; left: -50%;
  width: 200%; height: 200%;
  background:
    radial-gradient(circle at 25% 35%, rgba(255,255,255,0.12) 0%, transparent 50%),
    radial-gradient(circle at 75% 65%, rgba(255,255,255,0.08) 0%, transparent 40%),
    radial-gradient(circle at 50% 80%, rgba(255,255,255,0.05) 0%, transparent 30%);
  animation: floatSlow 25s ease-in-out infinite;
  pointer-events: none;
}
.cover-section::after {
  content: '';
  position: absolute;
  bottom: 0; left: 0; right: 0;
  height: 100px;
  background: linear-gradient(to top, var(--bg), transparent);
  pointer-events: none;
}
.cover-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  position: relative;
  z-index: 1;
  animation: fadeInUp 0.8s ease;
}
.cover-image {
  max-width: 680px;
  margin: 0 auto 2.5rem;
  border-radius: 20px;
  overflow: hidden;
  box-shadow: 0 20px 60px rgba(0,0,0,0.25);
  transition: transform 0.5s var(--transition);
  position: relative;
}
.cover-image::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: 20px;
  box-shadow: inset 0 0 30px rgba(0,0,0,0.1);
  pointer-events: none;
}
.cover-image:hover { transform: scale(1.02) translateY(-4px); }
.cover-image img { width: 100%; height: auto; display: block; }
.cover-badge {
  display: inline-block;
  padding: 0.4rem 1.5rem;
  background: rgba(255,255,255,0.15);
  border: 1px solid rgba(255,255,255,0.2);
  border-radius: 25px;
  font-size: 0.82rem;
  font-weight: 600;
  margin-bottom: 1.8rem;
  backdrop-filter: blur(8px);
  letter-spacing: 0.05em;
}
.cover-title {
  font-size: 2.6rem;
  font-weight: 900;
  line-height: 1.25;
  margin-bottom: 1rem;
  letter-spacing: -0.03em;
  text-shadow: 0 2px 20px rgba(0,0,0,0.1);
}
.cover-subtitle { font-size: 1.1rem; opacity: 0.85; font-weight: 300; margin-bottom: 1rem; }
.cover-company { font-size: 0.92rem; opacity: 0.7; font-weight: 400; margin-bottom: 0.5rem; }
.cover-reading-time {
  display: inline-block;
  padding: 0.3rem 1rem;
  background: rgba(255,255,255,0.1);
  border-radius: 15px;
  font-size: 0.8rem;
  opacity: 0.75;
  margin-top: 0.8rem;
}

.index-section {
  max-width: var(--max-width);
  margin: 2.5rem auto 3rem;
  padding: 0 2rem;
  position: relative;
  z-index: 2;
}
.section-label {
  font-family: var(--font-en);
  font-size: 0.7rem;
  font-weight: 700;
  color: var(--accent);
  letter-spacing: 0.15em;
  text-transform: uppercase;
  margin-bottom: 1rem;
}
.index-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.8rem;
}
.index-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  padding: 1.2rem 0.8rem;
  background: var(--bg-white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  text-decoration: none;
  color: var(--text);
  transition: all 0.35s var(--transition);
  text-align: center;
  box-shadow: var(--shadow-sm);
  position: relative;
  overflow: hidden;
}
.index-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: var(--gradient-main);
  opacity: 0;
  transition: opacity 0.3s;
}
.index-card:hover {
  border-color: var(--accent-light);
  box-shadow: var(--shadow-card-hover);
  transform: translateY(-5px);
}
.index-card:hover::before { opacity: 1; }
.index-num {
  font-family: var(--font-en);
  font-size: 0.62rem;
  font-weight: 700;
  color: var(--accent);
  letter-spacing: 0.15em;
}
.index-icon {
  font-size: 1.8rem;
  animation: bounce-subtle 3s ease-in-out infinite;
}
.index-card:nth-child(1) .index-icon { animation-delay: 0s; }
.index-card:nth-child(2) .index-icon { animation-delay: 0.3s; }
.index-card:nth-child(3) .index-icon { animation-delay: 0.6s; }
.index-card:nth-child(4) .index-icon { animation-delay: 0.9s; }
.index-title { font-size: 0.82rem; font-weight: 700; }
.index-desc { font-size: 0.72rem; color: var(--text-muted); line-height: 1.4; }

.content-section {
  max-width: var(--max-width);
  margin: 4rem auto;
  padding: 0 2rem;
}
.section-header { margin-bottom: 2.5rem; }
.section-tag {
  display: inline-block;
  padding: 0.3rem 0.9rem;
  background: var(--gradient-card);
  border: 1px solid var(--border);
  color: var(--accent);
  border-radius: 20px;
  font-family: var(--font-en);
  font-size: 0.65rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  margin-bottom: 0.8rem;
}
.section-header h2 {
  font-size: 1.55rem;
  font-weight: 800;
  margin-bottom: 0.4rem;
  letter-spacing: -0.02em;
}
.section-header p {
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 400;
  line-height: 1.6;
}

.insight-card {
  background: var(--bg-white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2.5rem;
  margin-bottom: 2rem;
  box-shadow: var(--shadow);
  position: relative;
  overflow: hidden;
  transition: all 0.3s var(--transition);
}
.insight-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 4px;
  background: var(--gradient-main);
}
.insight-card:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-2px);
}
.insight-card h3 { font-size: 1.2rem; font-weight: 800; margin-bottom: 0.3rem; }
.insight-card img {
  max-width: 100%;
  height: auto;
  display: block;
  margin: 1rem auto;
  border-radius: var(--radius-sm);
}
.insight-subtitle { color: var(--text-secondary); font-size: 0.88rem; margin-bottom: 2rem; }

.insight-stats {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1rem;
  margin-bottom: 2rem;
}
.stat-item {
  text-align: center;
  padding: 1.5rem 1rem;
  background: var(--gradient-soft);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  transition: all 0.35s var(--transition);
}
.stat-item:hover { box-shadow: var(--shadow); transform: translateY(-3px); }
.stat-icon { font-size: 2.2rem; margin-bottom: 0.5rem; animation: bounce-subtle 2.5s ease-in-out infinite; }
.stat-label { font-size: 0.88rem; font-weight: 700; margin-bottom: 0.2rem; }
.stat-desc { font-size: 0.74rem; color: var(--text-muted); line-height: 1.4; }

.insight-keywords { display: flex; flex-wrap: wrap; gap: 0.5rem; }
.keyword {
  padding: 0.35rem 1rem;
  background: var(--gradient-card);
  border: 1px solid var(--border);
  color: var(--accent-dark);
  border-radius: 20px;
  font-size: 0.76rem;
  font-weight: 600;
  transition: all 0.25s var(--transition);
}
.keyword:hover { background: var(--accent); color: white; border-color: var(--accent); }

.insight-courses { margin-top: 2.5rem; }
.insight-courses h3 { font-size: 1.1rem; font-weight: 700; margin-bottom: 0.3rem; }
.courses-subtitle { color: var(--text-secondary); font-size: 0.85rem; margin-bottom: 1.5rem; }
.course-grid-4 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1rem;
}
.course-mini-card {
  background: var(--bg-white);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 1.5rem;
  transition: all 0.35s var(--transition);
  position: relative;
  overflow: hidden;
}
.course-mini-card::after {
  content: '';
  position: absolute;
  bottom: 0; left: 0; right: 0;
  height: 3px;
  background: var(--gradient-main);
  opacity: 0;
  transition: opacity 0.3s;
}
.course-mini-card:hover {
  border-color: var(--accent-light);
  box-shadow: var(--shadow-lg);
  transform: translateY(-4px);
}
.course-mini-card:hover::after { opacity: 1; }
.course-mini-card img {
  width: 100%;
  height: 100px;
  object-fit: cover;
  border-radius: 8px;
  margin-bottom: 0.6rem;
}
.mini-icon { font-size: 1.8rem; margin-bottom: 0.6rem; animation: wiggle 4s ease-in-out infinite; }
.course-mini-card h4 { font-size: 0.9rem; font-weight: 700; margin-bottom: 0.3rem; line-height: 1.4; }
.course-mini-card p { font-size: 0.78rem; color: var(--text-secondary); margin-bottom: 0.6rem; line-height: 1.5; }
.mini-time { font-size: 0.72rem; color: var(--text-muted); }
.mini-link {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  margin-top: 0.6rem;
  color: var(--accent);
  font-size: 0.8rem;
  font-weight: 600;
  text-decoration: none;
  transition: all 0.25s var(--transition);
}
.mini-link:hover { color: var(--accent-dark); gap: 0.5rem; }

.new-highlight {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.2rem;
  margin-bottom: 2rem;
}
.new-highlight-card {
  background: var(--bg-white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  box-shadow: var(--shadow);
  transition: all 0.35s var(--transition);
  position: relative;
  overflow: hidden;
}
.new-highlight-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; bottom: 0;
  width: 4px;
  background: var(--gradient-main);
  opacity: 0;
  transition: opacity 0.3s;
}
.new-highlight-card:hover { box-shadow: var(--shadow-card-hover); transform: translateY(-3px); }
.new-highlight-card:hover::before { opacity: 1; }
.new-highlight-card img {
  width: 100%;
  height: 120px;
  object-fit: cover;
  border-radius: 8px;
  margin-bottom: 0.8rem;
}
.highlight-badge {
  display: inline-block;
  padding: 0.25rem 0.8rem;
  background: var(--gradient-main);
  color: white;
  border-radius: 10px;
  font-size: 0.68rem;
  font-weight: 700;
  margin-bottom: 1rem;
}
.new-highlight-card h3 { font-size: 1.02rem; font-weight: 700; margin-bottom: 0.5rem; }
.new-highlight-card > p { font-size: 0.82rem; color: var(--text-secondary); margin-bottom: 1.2rem; line-height: 1.6; }
.highlight-courses { display: flex; flex-direction: column; gap: 0.8rem; }
.h-course {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  flex-wrap: wrap;
  padding: 0.8rem 1rem;
  background: var(--bg-warm);
  border-radius: var(--radius-xs);
  transition: all 0.25s var(--transition);
}
.h-course:hover { background: var(--gradient-card); transform: translateX(4px); }
.h-title { font-size: 0.82rem; font-weight: 600; flex: 1; }
.h-time { font-size: 0.72rem; color: var(--text-muted); }

.new-summary {
  text-align: center;
  padding: 2rem;
  background: var(--gradient-soft);
  border: 1px solid var(--border-light);
  border-radius: var(--radius);
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.7;
}
.new-summary strong { color: var(--accent); font-weight: 700; }

.cta-primary {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.75rem 1.6rem;
  background: var(--gradient-main);
  background-size: 200% 200%;
  animation: gradientShift 5s ease infinite;
  color: white;
  border: none;
  border-radius: 28px;
  font-size: 0.88rem;
  font-weight: 700;
  text-decoration: none;
  cursor: pointer;
  transition: all 0.3s var(--transition);
  box-shadow: 0 4px 18px rgba(124,108,240,0.25);
  position: relative;
  overflow: hidden;
}
.cta-primary:hover {
  transform: translateY(-3px) scale(1.02);
  box-shadow: 0 8px 32px rgba(124,108,240,0.35);
}
.cta-primary .cta-arrow { transition: transform 0.3s var(--transition); display: inline-block; }
.cta-primary:hover .cta-arrow { transform: translateX(5px); }

.cta-banner {
  background: var(--gradient-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.8rem 2rem;
  text-align: center;
  margin: 2.5rem 0;
  animation: pulse-glow 4s ease-in-out infinite;
}
.cta-banner:hover { box-shadow: var(--shadow-lg); }
.cta-banner p { font-size: 0.92rem; color: var(--text-secondary); margin-bottom: 1rem; line-height: 1.6; }
.cta-banner strong { color: var(--accent); }
.cta-buttons-row {
  display: flex;
  gap: 0.6rem;
  justify-content: center;
  flex-wrap: wrap;
  margin-top: 1rem;
}

.curation-header {
  background: var(--bg-white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  margin-bottom: 1.2rem;
  box-shadow: var(--shadow);
  position: relative;
  overflow: hidden;
}
.curation-header::before {
  content: '';
  position: absolute;
  top: 0; left: 0; bottom: 0;
  width: 4px;
  background: var(--gradient-main);
}
.curation-header h3 { font-size: 1.02rem; font-weight: 700; margin-bottom: 1rem; padding-left: 0.8rem; }
.curation-tags { display: flex; gap: 0.5rem; flex-wrap: wrap; padding-left: 0.8rem; }
.curation-tag {
  padding: 0.35rem 1rem;
  background: var(--gradient-main);
  color: white;
  border-radius: 20px;
  font-size: 0.76rem;
  font-weight: 600;
  transition: all 0.2s;
}
.curation-tag:hover { transform: scale(1.05); }

.curation-list { display: flex; flex-direction: column; gap: 0.7rem; }
.curation-rich-item {
  display: flex;
  gap: 1.2rem;
  padding: 1.3rem 1.5rem;
  background: var(--bg-white);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  transition: all 0.35s var(--transition);
  align-items: flex-start;
  position: relative;
  overflow: hidden;
}
.curation-rich-item::before {
  content: '';
  position: absolute;
  left: 0; top: 0; bottom: 0;
  width: 3px;
  background: var(--gradient-main);
  opacity: 0;
  transition: opacity 0.3s;
}
.curation-rich-item:hover {
  border-color: var(--accent-light);
  box-shadow: var(--shadow);
  transform: translateX(6px);
}
.curation-rich-item:hover::before { opacity: 1; }
.curation-rank {
  font-family: var(--font-en);
  font-size: 1.2rem;
  font-weight: 900;
  background: var(--gradient-main);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  min-width: 35px;
  text-align: center;
  padding-top: 0.2rem;
  animation: sparkle 2.5s ease-in-out infinite;
}
.curation-rich-info { flex: 1; }
.curation-rich-title {
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--text);
  text-decoration: none;
  line-height: 1.4;
  display: block;
  margin-bottom: 0.35rem;
  transition: color 0.2s;
}
.curation-rich-title:hover { color: var(--accent); }
.curation-rich-meta {
  display: flex;
  gap: 0.6rem;
  font-size: 0.73rem;
  color: var(--text-muted);
  margin-bottom: 0.5rem;
  flex-wrap: wrap;
}
.curation-rich-meta span { display: inline-flex; align-items: center; gap: 0.15rem; }

.course-badge {
  display: inline-block;
  padding: 0.15rem 0.5rem;
  border-radius: 8px;
  font-size: 0.65rem;
  font-weight: 700;
  margin-right: 0.3rem;
  margin-bottom: 0.3rem;
}
.badge-popular { background: #fef3c7; color: #92400e; }
.badge-shortest { background: #dbeafe; color: #1e40af; }
.badge-top-rated { background: #d1fae5; color: #065f46; }
.badge-new { background: #ede9fe; color: #5b21b6; }
.badge-essential { background: #fce7f3; color: #9d174d; }

.curation-rich-comment {
  font-size: 0.78rem;
  color: var(--text-secondary);
  line-height: 1.55;
  padding: 0.6rem 0.8rem;
  background: var(--bg-warm);
  border-left: 3px solid var(--accent-light);
  border-radius: 0 var(--radius-xs) var(--radius-xs) 0;
  margin-bottom: 0.5rem;
}
.curation-rich-comment::before { content: '💡 '; }

.curation-rich-cta {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.4rem 1rem;
  background: var(--gradient-main);
  background-size: 200% 200%;
  animation: gradientShift 6s ease infinite;
  color: white;
  border-radius: 18px;
  font-size: 0.75rem;
  font-weight: 600;
  text-decoration: none;
  transition: all 0.3s var(--transition);
}
.curation-rich-cta:hover {
  box-shadow: 0 4px 16px rgba(124,108,240,0.3);
  transform: translateY(-2px);
}

.curation-note {
  text-align: center;
  font-size: 0.78rem;
  color: var(--text-muted);
  margin-top: 1.2rem;
  padding: 1rem;
  background: var(--bg-warm);
  border-radius: var(--radius-xs);
}

.curation-banner-image {
  width: 100%;
  border-radius: var(--radius);
  overflow: hidden;
  margin-bottom: 1.5rem;
  box-shadow: var(--shadow-sm);
}
.curation-banner-image img {
  width: 100%;
  height: 180px;
  object-fit: cover;
  display: block;
  transition: transform 0.4s var(--transition);
}
.curation-banner-image:hover img { transform: scale(1.03); }

.section-illustration {
  width: 100%;
  border-radius: var(--radius);
  overflow: hidden;
  margin-bottom: 2rem;
  box-shadow: var(--shadow);
  transition: all 0.4s var(--transition);
}
.section-illustration:hover { box-shadow: var(--shadow-lg); transform: translateY(-2px); }
.section-illustration img { width: 100%; height: auto; display: block; transition: transform 0.5s var(--transition); }
.section-illustration:hover img { transform: scale(1.02); }

.closing-template {
  text-align: center;
  padding: 3rem 2rem;
  background: var(--gradient-soft);
  position: relative;
}
.closing-template::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: var(--gradient-main);
}
.closing-template h2 {
  font-size: 1.3rem;
  background: var(--gradient-main);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 1.2rem;
  font-weight: 800;
}
.closing-template p {
  font-size: 0.88rem;
  color: var(--text-secondary);
  margin-bottom: 0.8rem;
  line-height: 1.8;
}
.closing-template .closing-emoji {
  font-size: 2rem;
  margin-bottom: 1rem;
  display: block;
}

.closing-section {
  background: var(--gradient-soft);
  padding: 4rem 2rem;
  text-align: center;
  margin-top: 4rem;
  position: relative;
}
.closing-section::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: var(--gradient-main);
}
.closing-inner { max-width: var(--max-width); margin: 0 auto; }
.closing-illustration {
  max-width: 600px;
  margin: 0 auto 2.5rem;
  border-radius: var(--radius);
  overflow: hidden;
  opacity: 0.9;
  transition: all 0.4s var(--transition);
}
.closing-illustration:hover { opacity: 1; }
.closing-illustration img { width: 100%; height: auto; display: block; }

.letter-footer {
  padding: 2.5rem 2rem;
  text-align: center;
  background: var(--bg-white);
  border-top: 1px solid var(--border-light);
}
.footer-inner { max-width: var(--max-width); margin: 0 auto; }
.footer-actions {
  display: flex;
  justify-content: center;
  gap: 0.6rem;
  margin-bottom: 1rem;
}
.footer-links {
  display: flex;
  justify-content: center;
  gap: 2rem;
  margin-bottom: 1rem;
}
.footer-link {
  color: var(--text-muted);
  font-size: 0.82rem;
  text-decoration: none;
  transition: color 0.2s;
}
.footer-link:hover { color: var(--accent); }
.footer-copyright { font-size: 0.72rem; color: var(--text-muted); }

.btn-explorer {
  padding: 0.45rem 1rem;
  border: 1px solid var(--accent);
  background: transparent;
  color: var(--accent);
  border-radius: 25px;
  cursor: pointer;
  font-size: 0.78rem;
  font-weight: 600;
  transition: all 0.3s var(--transition);
  text-decoration: none;
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
}
.btn-explorer:hover { background: var(--accent); color: white; box-shadow: var(--shadow); }

.scroll-to-top {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--gradient-main);
  color: white;
  border: none;
  cursor: pointer;
  font-size: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-lg);
  opacity: 0;
  visibility: hidden;
  transform: translateY(10px);
  transition: all 0.3s var(--transition);
  z-index: 90;
}
.scroll-to-top.visible { opacity: 1; visibility: visible; transform: translateY(0); }
.scroll-to-top:hover { transform: translateY(-3px) scale(1.1); box-shadow: var(--shadow-glow); }

.side-nav {
  position: fixed;
  right: 1.5rem;
  top: 50%;
  transform: translateY(-50%);
  z-index: 80;
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
  opacity: 0;
  visibility: hidden;
  transition: all 0.4s var(--transition);
}
.side-nav.visible { opacity: 1; visibility: visible; }
.side-nav-item {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.45rem 0.7rem;
  background: var(--bg-glass-strong);
  backdrop-filter: blur(12px);
  border: 1px solid var(--border);
  border-radius: 20px;
  text-decoration: none;
  color: var(--text-muted);
  font-size: 0.7rem;
  font-weight: 500;
  transition: all 0.25s var(--transition);
  cursor: pointer;
  white-space: nowrap;
}
.side-nav-item:hover { border-color: var(--accent); color: var(--accent); transform: translateX(-4px); box-shadow: var(--shadow); }
.side-nav-item.active { background: var(--accent); color: white; border-color: var(--accent); }
.side-nav-icon { font-size: 0.85rem; }

.letter-loading {
  text-align: center;
  padding: 6rem 2rem;
  color: var(--text-muted);
}
.letter-loading-icon {
  font-size: 3rem;
  margin-bottom: 1.5rem;
  animation: bounce-subtle 1.5s ease-in-out infinite;
}
.letter-loading-text {
  font-size: 0.95rem;
  font-weight: 500;
  transition: opacity 0.3s;
}
.letter-loading-bar {
  width: 200px;
  height: 4px;
  background: var(--border);
  border-radius: 2px;
  margin: 1.5rem auto 0;
  overflow: hidden;
}
.letter-loading-fill {
  height: 100%;
  background: var(--gradient-main);
  border-radius: 2px;
  width: 0%;
  transition: width 0.4s ease;
}

.ai-comment {
  font-size: 0.75rem;
  padding: 0.4rem 0.6rem;
  background: #f5f3ff;
  border-left: 3px solid #a78bfa;
  border-radius: 0 6px 6px 0;
  margin-bottom: 0.4rem;
  line-height: 1.5;
  color: var(--text-secondary);
}

.animate-on-scroll {
  opacity: 0;
  transform: translateY(24px);
  transition: all 0.65s var(--transition);
}
.animate-on-scroll.visible { opacity: 1; transform: translateY(0); }
.animate-on-scroll:nth-child(2) { transition-delay: 0.08s; }
.animate-on-scroll:nth-child(3) { transition-delay: 0.16s; }
.animate-on-scroll:nth-child(4) { transition-delay: 0.24s; }

[data-ko][data-en] { transition: opacity 0.15s ease; }

@media (max-width: 900px) {
  .side-nav {
    position: fixed;
    right: auto; left: 0;
    top: auto; bottom: 0;
    transform: none;
    flex-direction: row;
    width: 100%;
    justify-content: center;
    padding: 0.5rem;
    background: var(--bg-glass-strong);
    backdrop-filter: blur(16px);
    border-top: 1px solid var(--border-light);
    gap: 0.3rem;
    border-radius: 0;
  }
  .side-nav-item .side-nav-label { display: none; }
  .side-nav-item { padding: 0.4rem 0.6rem; border-radius: 15px; }
}

@media (max-width: 768px) {
  .cover-title { font-size: 1.7rem; }
  .cover-section { padding: 3rem 1.5rem 3.5rem; min-height: 420px; }
  .cover-image { max-width: 100%; }
  .index-grid { grid-template-columns: repeat(2, 1fr); }
  .insight-stats { grid-template-columns: 1fr; }
  .course-grid-4 { grid-template-columns: 1fr; }
  .new-highlight { grid-template-columns: 1fr; }
  .content-section { margin: 2.5rem auto; padding: 0 1.5rem; }
  .insight-card { padding: 1.5rem; }
  .curation-rich-item { flex-direction: column; padding: 1rem 1.2rem; }
  .curation-rank { min-width: auto; }
  .header-actions { gap: 0.3rem; }
  .btn-letter { font-size: 0.7rem; padding: 0.35rem 0.7rem; }
  .section-header h2 { font-size: 1.25rem; }
  .cta-banner { padding: 1.2rem 1rem; }
  .cta-primary { padding: 0.65rem 1.2rem; font-size: 0.82rem; }
  .scroll-to-top { bottom: 1.2rem; right: 1.2rem; width: 40px; height: 40px; }
  .curation-banner-image img { height: 120px; }
}

@media (max-width: 480px) {
  .header-inner { padding: 0 1rem; }
  .cover-title { font-size: 1.4rem; }
  .lang-toggle { display: none; }
  .index-grid { grid-template-columns: 1fr; }
}

@media print {
  .letter-header, .letter-footer, .lang-toggle,
  .scroll-progress, .scroll-to-top, .side-nav,
  .cta-banner, .cta-primary, .btn-explorer { display: none !important; }
  body { -webkit-print-color-adjust: exact; print-color-adjust: exact; background: white; }
  body::before { display: none; }
  @page { size: A4; margin: 15mm 12mm; }
  .cover-section { page-break-after: always; min-height: 90vh; animation: none !important; background: #7c6cf0 !important; }
  .index-section { page-break-before: always; page-break-after: always; }
  .content-section { page-break-before: always; }
  .insight-card, .course-mini-card, .new-highlight-card, .curation-rich-item, .curation-header { page-break-inside: avoid; }
  .closing-template, .closing-section { page-break-before: always; }
  * { animation: none !important; transition: none !important; }
  .cover-inner, .index-section, .content-section, .closing-inner, .footer-inner { max-width: 100% !important; }
  a[data-slug]::after { content: " (" attr(href) ")"; font-size: 0.6rem; color: #888; word-break: break-all; }
  .section-illustration, .closing-illustration, .curation-banner-image { box-shadow: none !important; page-break-inside: avoid; }
}

/* ═══ Mobile Bottom Bar (INDEX + Top + Lang) ═══ */
.mobile-bottom-bar {
  display: none;
}

@media (max-width: 900px) {
  /* Hide desktop top button on mobile */
  .scroll-to-top.desktop-only { display: none !important; }

  /* Hide header lang toggle on mobile - moved to bottom bar */
  .lang-toggle { display: none; }

  /* Mobile bottom bar */
  .mobile-bottom-bar {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    z-index: 90;
    display: none;
    background: rgba(255,255,255,0.92);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border-top: 1px solid var(--border-light);
    padding: 0.4rem 0.5rem;
    padding-bottom: calc(0.4rem + env(safe-area-inset-bottom, 0px));
    gap: 0;
    align-items: center;
    justify-content: center;
  }
  .mobile-bottom-bar.visible {
    display: flex;
  }

  .mobile-bar-item {
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 0.4rem 0.65rem;
    background: transparent;
    border: 1px solid var(--border);
    border-radius: 15px;
    color: var(--text-muted);
    font-size: 0.7rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s;
    white-space: nowrap;
    font-family: var(--font);
    gap: 0.2rem;
    min-width: 36px;
    min-height: 36px;
  }
  .mobile-bar-item:hover,
  .mobile-bar-item:active {
    border-color: var(--accent);
    color: var(--accent);
  }
  .mobile-bar-item.active {
    background: var(--accent);
    color: white;
    border-color: var(--accent);
  }

  /* Side nav becomes part of bottom bar */
  .side-nav {
    position: fixed;
    right: auto;
    left: 0;
    top: auto;
    bottom: 0;
    transform: none;
    flex-direction: row;
    width: 100%;
    justify-content: center;
    padding: 0.4rem 0.5rem;
    padding-bottom: calc(0.4rem + env(safe-area-inset-bottom, 0px));
    background: rgba(255,255,255,0.92);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border-top: 1px solid var(--border-light);
    gap: 0.25rem;
    border-radius: 0;
    z-index: 91;
  }
  .side-nav .side-nav-label { display: none; }
  .side-nav-item {
    padding: 0.4rem 0.55rem;
    border-radius: 12px;
    font-size: 0.65rem;
    min-width: 36px;
    min-height: 36px;
    justify-content: center;
  }

  /* Hide mobile-bottom-bar when side-nav is visible */
  .side-nav.visible ~ .mobile-bottom-bar { display: none; }

  /* Mobile link copy button */
  .btn-letter#btn-copy-link {
    font-size: 0.7rem;
    padding: 0.35rem 0.7rem;
  }
}

/* ═══ Desktop: hide mobile bar ═══ */
@media (min-width: 901px) {
  .mobile-bottom-bar { display: none !important; }
}

/* ═══ Link Copy Toast ═══ */
.copy-toast {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%) scale(0.9);
  padding: 1rem 2rem;
  background: rgba(26,26,46,0.95);
  color: white;
  border-radius: 16px;
  font-size: 0.9rem;
  font-weight: 600;
  z-index: 2000;
  opacity: 0;
  transition: all 0.3s var(--transition);
  pointer-events: none;
  text-align: center;
}
.copy-toast.show {
  opacity: 1;
  transform: translate(-50%, -50%) scale(1);
}

/* ═══ Scroll Down Indicator (Cover) ═══ */
.scroll-indicator {
  position: absolute;
  bottom: 2rem;
  left: 50%;
  transform: translateX(-50%);
  z-index: 2;
  animation: bounce-subtle 2s ease-in-out infinite;
  opacity: 0.6;
  font-size: 1.5rem;
  cursor: pointer;
  transition: opacity 0.3s;
}
.scroll-indicator:hover { opacity: 1; }

/* ═══ Course Card Thumbnail Ratio ═══ */
.course-mini-card img,
.new-highlight-card img {
  width: 100%;
  height: 0;
  padding-bottom: 56.25%;
  object-fit: cover;
  border-radius: 8px;
  margin-bottom: 0.6rem;
  position: relative;
}
.course-mini-card a > img,
.new-highlight-card a > img {
  height: auto;
  padding-bottom: 0;
  aspect-ratio: 16/9;
}

/* ═══ Touch Feedback ═══ */
@media (hover: none) {
  .course-mini-card:active,
  .new-highlight-card:active,
  .curation-rich-item:active,
  .index-card:active,
  .cta-primary:active {
    transform: scale(0.97);
    transition: transform 0.1s;
  }
}

/* ═══ CTA Pulse Enhancement ═══ */
.cta-primary {
  position: relative;
}
.cta-primary::after {
  content: '';
  position: absolute;
  inset: -3px;
  border-radius: 30px;
  background: var(--gradient-main);
  opacity: 0;
  z-index: -1;
  animation: ctaPulse 3s ease-in-out infinite;
}
@keyframes ctaPulse {
  0%, 100% { opacity: 0; transform: scale(1); }
  50% { opacity: 0.15; transform: scale(1.05); }
}

/* ═══ Course Card Hover Zoom ═══ */
.course-mini-card a > img,
.new-highlight-card a > img {
  transition: transform 0.4s var(--transition);
}
.course-mini-card:hover a > img,
.new-highlight-card:hover a > img {
  transform: scale(1.05);
}