/* ============================================================
   미래역량AI연구소 학습 플랫폼 — main.css
   전역 스타일 · 화이트 테마 · CSS 변수 · 타이포그래피 · 반응형 그리드 · 애니메이션
   ============================================================ */

/* ── 1. CSS 커스텀 변수 ── */
:root {
  /* 컬러 팔레트 */
  --color-primary:        #1E40AF;
  --color-primary-light:  #3B82F6;
  --color-primary-dark:   #1E3A8A;
  --color-secondary:      #7C3AED;
  --color-secondary-light:#A78BFA;
  --color-accent:         #059669;
  --color-accent-light:   #10B981;

  /* 배경 - 화이트 테마 */
  --bg-base:              #FFFFFF;
  --bg-surface:           #FFFFFF;
  --bg-surface-2:         #F8FAFF;
  --bg-surface-3:         #EEF2FF;
  --bg-glass:             rgba(255, 255, 255, 0.92);
  --bg-glass-light:       rgba(59, 130, 246, 0.06);

  /* 텍스트 - 최고 대비 */
  --text-primary:         #0F172A;
  --text-secondary:       #334155;
  --text-muted:           #64748B;
  --text-accent:          #1D4ED8;

  /* 테두리 - 유색 */
  --border-color:         rgba(59, 130, 246, 0.2);
  --border-color-hover:   rgba(99, 102, 241, 0.45);

  /* 그림자 */
  --shadow-sm:            0 1px 4px rgba(30, 64, 175, 0.08);
  --shadow-md:            0 4px 20px rgba(30, 64, 175, 0.12);
  --shadow-lg:            0 8px 40px rgba(30, 64, 175, 0.16);
  --shadow-glow-blue:     0 0 32px rgba(59, 130, 246, 0.25);
  --shadow-glow-purple:   0 0 32px rgba(124, 58, 237, 0.2);

  /* 타이포그래피 */
  --font-sans:            'Noto Sans KR', 'Inter', system-ui, sans-serif;
  --font-mono:            'JetBrains Mono', 'Fira Code', monospace;
  --fs-xs:                0.75rem;    /* 12px */
  --fs-sm:                0.875rem;   /* 14px */
  --fs-base:              1rem;       /* 16px */
  --fs-md:                1.125rem;   /* 18px */
  --fs-lg:                1.25rem;    /* 20px */
  --fs-xl:                1.5rem;     /* 24px */
  --fs-2xl:               1.875rem;   /* 30px */
  --fs-3xl:               2.25rem;    /* 36px */
  --fs-4xl:               3rem;       /* 48px */
  --fw-regular:           400;
  --fw-medium:            500;
  --fw-semibold:          600;
  --fw-bold:              700;
  --fw-extrabold:         800;
  --lh-tight:             1.25;
  --lh-normal:            1.6;
  --lh-relaxed:           1.75;

  /* 간격 (8px 기반) */
  --space-1:              0.25rem;    /* 4px */
  --space-2:              0.5rem;     /* 8px */
  --space-3:              0.75rem;    /* 12px */
  --space-4:              1rem;       /* 16px */
  --space-5:              1.25rem;    /* 20px */
  --space-6:              1.5rem;     /* 24px */
  --space-8:              2rem;       /* 32px */
  --space-10:             2.5rem;     /* 40px */
  --space-12:             3rem;       /* 48px */
  --space-16:             4rem;       /* 64px */
  --space-20:             5rem;       /* 80px */

  /* 반경 */
  --radius-sm:            4px;
  --radius-md:            8px;
  --radius-lg:            12px;
  --radius-xl:            16px;
  --radius-2xl:           24px;
  --radius-full:          9999px;

  /* 전환 */
  --transition-fast:      150ms ease;
  --transition-normal:    250ms ease;
  --transition-slow:      400ms ease;

  /* z-index 레이어 */
  --z-base:               0;
  --z-dropdown:           100;
  --z-sticky:             200;
  --z-modal:              300;
  --z-toast:              400;
  --z-tooltip:            500;

  /* 레이아웃 */
  --max-width:            1280px;
  --nav-height:           64px;
  --sidebar-width:        320px;
}

/* ── 2. CSS 리셋 & 기반 ── */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-sans);
  font-size: var(--fs-base);
  font-weight: var(--fw-regular);
  line-height: var(--lh-normal);
  color: var(--text-primary);
  background-color: #FFFFFF;
  min-height: 100vh;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

img, video, iframe {
  display: block;
  max-width: 100%;
}

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

button {
  font-family: inherit;
  cursor: pointer;
  border: none;
  background: none;
}

input, textarea, select {
  font-family: inherit;
  font-size: inherit;
}

ul, ol {
  list-style: none;
}

h1, h2, h3, h4, h5, h6 {
  font-weight: var(--fw-bold);
  line-height: var(--lh-tight);
  color: var(--text-primary);
}

/* ── 3. 타이포그래피 유틸리티 ── */
.text-xs     { font-size: var(--fs-xs); }
.text-sm     { font-size: var(--fs-sm); }
.text-base   { font-size: var(--fs-base); }
.text-md     { font-size: var(--fs-md); }
.text-lg     { font-size: var(--fs-lg); }
.text-xl     { font-size: var(--fs-xl); }
.text-2xl    { font-size: var(--fs-2xl); }
.text-3xl    { font-size: var(--fs-3xl); }
.text-4xl    { font-size: var(--fs-4xl); }

.font-medium    { font-weight: var(--fw-medium); }
.font-semibold  { font-weight: var(--fw-semibold); }
.font-bold      { font-weight: var(--fw-bold); }
.font-extrabold { font-weight: var(--fw-extrabold); }

.text-primary   { color: var(--text-primary); }
.text-secondary { color: var(--text-secondary); }
.text-muted     { color: var(--text-muted); }
.text-accent    { color: var(--text-accent); }
.text-green     { color: var(--color-accent-light); }
.text-purple    { color: var(--color-secondary-light); }

.text-center  { text-align: center; }
.text-right   { text-align: right; }
.text-left    { text-align: left; }

.leading-tight   { line-height: var(--lh-tight); }
.leading-relaxed { line-height: var(--lh-relaxed); }

/* 그라디언트 텍스트 */
.gradient-text {
  background: linear-gradient(135deg, var(--color-primary-light), var(--color-secondary-light));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.gradient-text-green {
  background: linear-gradient(135deg, var(--color-accent-light), var(--color-primary-light));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* ── 4. 레이아웃 ── */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin-inline: auto;
  padding-inline: var(--space-4);
}

@media (min-width: 640px)  { .container { padding-inline: var(--space-6); } }
@media (min-width: 1024px) { .container { padding-inline: var(--space-8); } }

.page-wrapper {
  padding-top: var(--nav-height);
  min-height: 100vh;
}

/* 섹션 간격 */
.section {
  padding-block: var(--space-16);
}
.section-sm {
  padding-block: var(--space-10);
}

.section-title {
  font-size: var(--fs-2xl);
  font-weight: var(--fw-bold);
  margin-bottom: var(--space-2);
}
.section-subtitle {
  font-size: var(--fs-base);
  color: var(--text-secondary);
  margin-bottom: var(--space-8);
}

/* ── 5. 반응형 그리드 ── */

/* 영상 카드 그리드 */
.video-grid {
  display: grid;
  gap: 16px;
  grid-template-columns: 1fr;
}
@media (min-width: 480px) {
  .video-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (min-width: 768px) {
  .video-grid { grid-template-columns: repeat(3, 1fr); gap: 16px; }
}
@media (min-width: 1024px) {
  .video-grid { grid-template-columns: repeat(4, 1fr); }
}
@media (min-width: 1280px) {
  .video-grid { grid-template-columns: repeat(5, 1fr); }
}

/* 카테고리 그리드 */
.category-grid {
  display: grid;
  gap: var(--space-4);
  grid-template-columns: repeat(2, 1fr);
}
@media (min-width: 480px) {
  .category-grid { grid-template-columns: repeat(3, 1fr); }
}
@media (min-width: 768px) {
  .category-grid { grid-template-columns: repeat(4, 1fr); }
}
@media (min-width: 1024px) {
  .category-grid { grid-template-columns: repeat(5, 1fr); }
}

/* 2열 레이아웃 (콘텐츠 + 사이드바) */
.content-with-sidebar {
  display: grid;
  gap: var(--space-8);
  grid-template-columns: 1fr;
}
@media (min-width: 1024px) {
  .content-with-sidebar {
    grid-template-columns: 1fr var(--sidebar-width);
    align-items: start;
  }
}

/* 통계 카드 그리드 */
.stats-grid {
  display: grid;
  gap: var(--space-4);
  grid-template-columns: repeat(2, 1fr);
}
@media (min-width: 768px) {
  .stats-grid { grid-template-columns: repeat(4, 1fr); }
}

/* ── 6. 플렉스 유틸리티 ── */
.flex          { display: flex; }
.flex-col      { flex-direction: column; }
.flex-wrap     { flex-wrap: wrap; }
.items-center  { align-items: center; }
.items-start   { align-items: flex-start; }
.items-end     { align-items: flex-end; }
.justify-center { justify-content: center; }
.justify-between { justify-content: space-between; }
.justify-end    { justify-content: flex-end; }
.gap-1   { gap: var(--space-1); }
.gap-2   { gap: var(--space-2); }
.gap-3   { gap: var(--space-3); }
.gap-4   { gap: var(--space-4); }
.gap-6   { gap: var(--space-6); }
.gap-8   { gap: var(--space-8); }
.flex-1  { flex: 1; }
.flex-shrink-0 { flex-shrink: 0; }

/* ── 7. 배경 & 카드 유틸리티 ── */
.bg-surface   { background: var(--bg-surface); }
.bg-surface-2 { background: var(--bg-surface-2); }
.bg-glass     { background: var(--bg-glass); backdrop-filter: blur(12px); -webkit-backdrop-filter: blur(12px); }

.card {
  background: #FFFFFF;
  border: 1.5px solid rgba(59, 130, 246, 0.18);
  border-radius: var(--radius-xl);
  padding: var(--space-6);
  box-shadow: 0 2px 12px rgba(30, 64, 175, 0.06);
}

.card-hover {
  transition: transform var(--transition-normal), box-shadow var(--transition-normal), border-color var(--transition-normal);
}
.card-hover:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 32px rgba(30, 64, 175, 0.14);
  border-color: rgba(99, 102, 241, 0.4);
}

/* ── 8. 구분선 ── */
.divider {
  height: 1px;
  background: var(--border-color);
  margin-block: var(--space-6);
}

/* ── 9. 배지 ── */
.badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: 2px var(--space-2);
  border-radius: var(--radius-full);
  font-size: var(--fs-xs);
  font-weight: var(--fw-semibold);
  white-space: nowrap;
}
.badge-blue   { background: rgba(59,130,246,0.1); color: #1D4ED8; border: 1px solid rgba(59,130,246,0.3); }
.badge-purple { background: rgba(124,58,237,0.08); color: #7C3AED; border: 1px solid rgba(124,58,237,0.25); }
.badge-green  { background: rgba(5,150,105,0.08); color: #059669; border: 1px solid rgba(5,150,105,0.25); }
.badge-orange { background: rgba(234,88,12,0.08); color: #D97706; border: 1px solid rgba(234,88,12,0.25); }
.badge-gray   { background: rgba(100,116,139,0.1); color: #334155; border: 1px solid rgba(100,116,139,0.2); }

/* ── 10. 스크롤바 커스텀 ── */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: #F1F5F9; }
::-webkit-scrollbar-thumb { background: #CBD5E1; border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: #94A3B8; }

/* ── 11. 애니메이션 키프레임 ── */
@keyframes fadeIn {
  from { opacity: 0; }
  to   { opacity: 1; }
}

@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(20px); }
  to   { opacity: 1; transform: translateY(0); }
}

@keyframes fadeInDown {
  from { opacity: 0; transform: translateY(-20px); }
  to   { opacity: 1; transform: translateY(0); }
}

@keyframes fadeInLeft {
  from { opacity: 0; transform: translateX(-20px); }
  to   { opacity: 1; transform: translateX(0); }
}

@keyframes slideUp {
  from { transform: translateY(100%); opacity: 0; }
  to   { transform: translateY(0); opacity: 1; }
}

@keyframes scaleIn {
  from { opacity: 0; transform: scale(0.95); }
  to   { opacity: 1; transform: scale(1); }
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50%       { opacity: 0.5; }
}

@keyframes spin {
  from { transform: rotate(0deg); }
  to   { transform: rotate(360deg); }
}

@keyframes shimmer {
  0%   { background-position: -200% 0; }
  100% { background-position: 200% 0; }
}

@keyframes gradientShift {
  0%   { background-position: 0% 50%; }
  50%  { background-position: 100% 50%; }
  100% { background-position: 0% 50%; }
}

@keyframes float {
  0%, 100% { transform: translateY(0); }
  50%       { transform: translateY(-8px); }
}

@keyframes glow {
  0%, 100% { box-shadow: var(--shadow-glow-blue); }
  50%       { box-shadow: var(--shadow-glow-purple); }
}

/* 애니메이션 클래스 */
.animate-fade-in     { animation: fadeIn 0.4s ease forwards; }
.animate-fade-in-up  { animation: fadeInUp 0.5s ease forwards; }
.animate-fade-in-down { animation: fadeInDown 0.4s ease forwards; }
.animate-scale-in    { animation: scaleIn 0.3s ease forwards; }
.animate-float       { animation: float 3s ease-in-out infinite; }
.animate-pulse       { animation: pulse 2s ease-in-out infinite; }
.animate-spin        { animation: spin 1s linear infinite; }
.animate-glow        { animation: glow 3s ease-in-out infinite; }

/* 딜레이 유틸리티 */
.delay-100 { animation-delay: 100ms; }
.delay-200 { animation-delay: 200ms; }
.delay-300 { animation-delay: 300ms; }
.delay-400 { animation-delay: 400ms; }
.delay-500 { animation-delay: 500ms; }

/* 스켈레톤 로딩 */
.skeleton {
  background: linear-gradient(90deg, #F1F5F9 25%, #E2E8F0 50%, #F1F5F9 75%);
  background-size: 200% 100%;
  animation: shimmer 1.5s infinite;
  border-radius: var(--radius-md);
}

/* ── 12. 반응형 유틸리티 ── */
.hidden         { display: none !important; }
.sr-only        { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0; }

@media (max-width: 639px) {
  .hidden-mobile { display: none !important; }
  .text-4xl { font-size: var(--fs-2xl); }
  .text-3xl { font-size: var(--fs-xl); }
}
@media (min-width: 640px) {
  .hidden-desktop { display: none !important; }
}
@media (max-width: 1023px) {
  .hidden-tablet { display: none !important; }
}

/* ── 13. 인터랙션 피드백 ── */
.interactive {
  transition: opacity var(--transition-fast), transform var(--transition-fast);
  cursor: pointer;
}
.interactive:hover  { opacity: 0.85; }
.interactive:active { transform: scale(0.97); }

/* ── 14. 포커스 링 ── */
:focus-visible {
  outline: 2px solid var(--color-primary-light);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}

/* ── 15. 선택 색상 ── */
::selection {
  background: rgba(99, 102, 241, 0.2);
  color: #0F172A;
}

/* ── 16. 스크롤 여백 (fixed nav 보정) ── */
[id] { scroll-margin-top: calc(var(--nav-height) + 16px); }

/* ── 17. 공통 섹션 헤더 ── */
.section-header {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  margin-bottom: var(--space-8);
  gap: var(--space-4);
  flex-wrap: wrap;
}

.section-header .view-all {
  font-size: var(--fs-sm);
  color: var(--color-primary-light);
  font-weight: var(--fw-medium);
  white-space: nowrap;
  transition: color var(--transition-fast);
}
.section-header .view-all:hover { color: var(--color-secondary-light); }

/* ── 18. 페이지 구분선 그라디언트 ── */
.gradient-divider {
  height: 1px;
  background: linear-gradient(90deg, transparent, rgba(99, 102, 241, 0.35), rgba(59, 130, 246, 0.25), transparent);
  margin-block: var(--space-12);
}

/* ── 19. 빈 상태 (empty state) ── */
.empty-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: var(--space-4);
  padding: var(--space-16) var(--space-8);
  text-align: center;
}

.empty-state-icon {
  font-size: 4rem;
  opacity: 0.5;
}

.empty-state-title {
  font-size: var(--fs-xl);
  font-weight: var(--fw-semibold);
  color: #334155;
}

.empty-state-desc {
  font-size: var(--fs-sm);
  color: #64748B;
  max-width: 360px;
}

/* ── 20. 로딩 오버레이 ── */
.loading-overlay {
  position: fixed;
  inset: 0;
  background: rgba(255, 255, 255, 0.85);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: var(--z-modal);
  backdrop-filter: blur(4px);
}

.spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--border-color);
  border-top-color: var(--color-primary-light);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

.spinner-sm {
  width: 20px;
  height: 20px;
  border-width: 2px;
}

/* ── 21. 히어로 그라디언트 배경 ── */
.hero-bg {
  background:
    radial-gradient(ellipse 80% 60% at 20% 40%, rgba(59, 130, 246, 0.12) 0%, transparent 60%),
    radial-gradient(ellipse 60% 50% at 80% 60%, rgba(124, 58, 237, 0.08) 0%, transparent 60%),
    linear-gradient(135deg, #EEF2FF 0%, #E0E7FF 30%, #F0F4FF 60%, #F8FAFF 100%);
  border-bottom: 1px solid rgba(99, 102, 241, 0.15);
}

/* ── 22. 구분선 그라디언트 테두리 ── */
.border-gradient {
  position: relative;
  border: 1.5px solid transparent;
  background: linear-gradient(#FFFFFF, #FFFFFF) padding-box,
              linear-gradient(135deg, var(--color-primary), var(--color-secondary)) border-box;
}

/* ── 23. 탭 인터페이스 기반 ── */
.tabs {
  display: flex;
  gap: var(--space-2);
  flex-wrap: wrap;
}

.tab-pane {
  display: none;
}
.tab-pane.active {
  display: block;
  animation: fadeIn 0.3s ease;
}

/* ── 24. 커스텀 체크박스 ── */
.custom-checkbox {
  position: relative;
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  cursor: pointer;
}
.custom-checkbox input[type="checkbox"] {
  width: 18px;
  height: 18px;
  accent-color: var(--color-primary-light);
  cursor: pointer;
}

/* ── 25. 구글 폰트 로드 (인라인 대체) ── */
@import url('https://fonts.googleapis.com/css2?family=Noto+Sans+KR:wght@400;500;600;700;800&family=Inter:wght@400;500;600;700;800&display=swap');

/* ── 26. 모바일 최적화 ── */
@media (max-width: 639px) {
  :root {
    --nav-height: 56px;
    --space-16: 3rem;
    --space-20: 4rem;
  }
  body { font-size: 15px; }
  .section { padding-block: 40px; }
  .section-sm { padding-block: 28px; }
  .card { padding: var(--space-4); }
  .btn { min-height: 44px; }
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
}