/* ============================
   CSS 변수 (테마)
   ============================ */
:root {
  --color-bg:              #ffffff;
  --color-surface:         #f8f9fa;
  --color-border:          #e9ecef;
  --color-text-primary:    #1a1a2e;
  --color-text-secondary:  #6c757d;
  --color-text-muted:      #adb5bd;
  --color-accent:          #2563eb;
  --color-accent-hover:    #1d4ed8;
  --color-accent-light:    #dbeafe;

  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI',
               'Apple SD Gothic Neo', 'Noto Sans KR', 'Malgun Gothic', sans-serif;

  --text-xs:   0.75rem;
  --text-sm:   0.875rem;
  --text-base: 1rem;
  --text-lg:   1.125rem;
  --text-xl:   1.25rem;
  --text-2xl:  1.5rem;
  --text-3xl:  1.875rem;
  --text-4xl:  2.25rem;
  --text-5xl:  3rem;

  --weight-normal: 400;
  --weight-medium: 500;
  --weight-semibold: 600;
  --weight-bold: 700;

  --spacing-xs:   0.5rem;
  --spacing-sm:   0.75rem;
  --spacing-md:   1rem;
  --spacing-lg:   1.5rem;
  --spacing-xl:   2rem;
  --spacing-2xl:  3rem;
  --spacing-section: 6rem;

  --max-width: 960px;
  --nav-height: 60px;

  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-full: 9999px;

  --shadow-sm:   0 1px 3px rgba(0, 0, 0, 0.08);
  --shadow-md:   0 4px 12px rgba(0, 0, 0, 0.08);
  --shadow-lg:   0 8px 24px rgba(0, 0, 0, 0.10);
  --shadow-card: 0 1px 3px rgba(0, 0, 0, 0.06), 0 4px 16px rgba(0, 0, 0, 0.06);
  --shadow-card-hover: 0 4px 8px rgba(0, 0, 0, 0.08), 0 12px 28px rgba(0, 0, 0, 0.10);

  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 400ms ease;
}

/* ============================
   CSS Reset
   ============================ */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: var(--nav-height);
}

body {
  font-family: var(--font-sans);
  font-size: var(--text-base);
  color: var(--color-text-primary);
  background-color: var(--color-bg);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

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

ul {
  list-style: none;
}

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

/* ============================
   공통 유틸리티
   ============================ */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-xl);
}

.section-title {
  font-size: var(--text-3xl);
  font-weight: var(--weight-bold);
  color: var(--color-text-primary);
  letter-spacing: -0.02em;
}

.section-subtitle {
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  color: var(--color-accent);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-top: var(--spacing-xs);
  margin-bottom: var(--spacing-2xl);
}

/* ============================
   버튼
   ============================ */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--spacing-xs);
  padding: 0.75rem var(--spacing-lg);
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
  cursor: pointer;
  transition: all var(--transition-base);
  white-space: nowrap;
}

.btn-primary {
  background-color: var(--color-accent);
  color: #ffffff;
  border: 2px solid var(--color-accent);
}

.btn-primary:hover {
  background-color: var(--color-accent-hover);
  border-color: var(--color-accent-hover);
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(37, 99, 235, 0.3);
}

.btn-outline {
  background-color: transparent;
  color: var(--color-text-primary);
  border: 2px solid var(--color-border);
}

.btn-outline:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  transform: translateY(-1px);
}

/* ============================
   네비게이션
   ============================ */
#nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  height: var(--nav-height);
  transition: background-color var(--transition-base),
              box-shadow var(--transition-base);
}

#nav.scrolled {
  background-color: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  box-shadow: 0 1px 0 var(--color-border);
}

.nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-xl);
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-logo {
  font-size: var(--text-lg);
  font-weight: var(--weight-bold);
  color: var(--color-accent);
  letter-spacing: 0.05em;
  transition: opacity var(--transition-fast);
}

.nav-logo:hover {
  opacity: 0.75;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--spacing-xl);
}

.nav-links a {
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  color: var(--color-text-secondary);
  position: relative;
  padding-bottom: 2px;
  transition: color var(--transition-fast);
}

.nav-links a::after {
  content: '';
  position: absolute;
  bottom: -2px;
  left: 0;
  right: 0;
  height: 2px;
  background-color: var(--color-accent);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--transition-base);
  border-radius: var(--radius-full);
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--color-text-primary);
}

.nav-links a.active::after,
.nav-links a:hover::after {
  transform: scaleX(1);
}

/* 언어 토글 */
.lang-toggle {
  display: flex;
  gap: 2px;
  padding: 3px;
  background: rgba(37, 99, 235, 0.06);
  border-radius: 10px;
  list-style: none;
}

.lang-btn {
  border: none;
  background: transparent;
  padding: 4px 11px;
  border-radius: 7px;
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  color: var(--color-text-secondary);
  cursor: pointer;
  font-family: inherit;
  transition: color var(--transition-fast),
              background-color var(--transition-fast);
}

.lang-btn:hover {
  color: var(--color-accent);
}

.lang-btn.active {
  background: var(--color-accent);
  color: #fff;
}

/* ============================
   Hero 섹션
   ============================ */
#hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  padding-top: var(--nav-height);
  background-color: var(--color-bg);
}

.hero-content {
  padding-top: var(--spacing-2xl);
  padding-bottom: var(--spacing-2xl);
}

.hero-badge {
  display: inline-block;
  padding: 0.375rem var(--spacing-sm);
  background-color: var(--color-accent-light);
  color: var(--color-accent);
  font-size: var(--text-xs);
  font-weight: var(--weight-semibold);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  border-radius: var(--radius-full);
  margin-bottom: var(--spacing-lg);
}

.hero-name {
  font-size: clamp(var(--text-4xl), 7vw, var(--text-5xl));
  font-weight: var(--weight-bold);
  letter-spacing: -0.03em;
  line-height: 1.15;
  margin-bottom: var(--spacing-lg);
  color: var(--color-text-primary);
}

.hero-tagline {
  font-size: var(--text-lg);
  color: var(--color-text-secondary);
  line-height: 1.8;
  max-width: 580px;
  margin-bottom: var(--spacing-2xl);
}

.hero-links {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-md);
}

/* ============================
   Education 섹션
   ============================ */
#education {
  padding: var(--spacing-section) 0;
  background-color: var(--color-surface);
}

.timeline {
  position: relative;
  padding-left: var(--spacing-xl);
}

.timeline::before {
  content: '';
  position: absolute;
  left: 0;
  top: 8px;
  bottom: 8px;
  width: 2px;
  background: linear-gradient(to bottom, var(--color-accent), var(--color-border));
  border-radius: var(--radius-full);
}

.timeline-item {
  position: relative;
  padding-bottom: var(--spacing-2xl);
}

.timeline-item:last-child {
  padding-bottom: 0;
}

.timeline-dot {
  position: absolute;
  left: calc(-1 * var(--spacing-xl) - 5px);
  top: 8px;
  width: 12px;
  height: 12px;
  background-color: var(--color-accent);
  border: 2px solid var(--color-bg);
  border-radius: 50%;
  box-shadow: 0 0 0 2px var(--color-accent);
}

.timeline-content {
  background-color: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--spacing-lg) var(--spacing-xl);
  box-shadow: var(--shadow-sm);
  transition: box-shadow var(--transition-base);
}

.timeline-content:hover {
  box-shadow: var(--shadow-md);
}

.edu-header {
  display: flex;
  align-items: baseline;
  flex-wrap: wrap;
  gap: var(--spacing-sm);
  margin-bottom: var(--spacing-xs);
}

.edu-school {
  font-size: var(--text-xl);
  font-weight: var(--weight-semibold);
  color: var(--color-text-primary);
}

.edu-period {
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  color: var(--color-accent);
  background-color: var(--color-accent-light);
  padding: 2px var(--spacing-xs);
  border-radius: var(--radius-sm);
  white-space: nowrap;
}

.edu-major {
  font-size: var(--text-base);
  font-weight: var(--weight-medium);
  color: var(--color-text-secondary);
  margin-bottom: var(--spacing-sm);
}

.edu-detail {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  line-height: 1.7;
}

/* ============================
   Projects 섹션
   ============================ */
#projects {
  padding: var(--spacing-section) 0;
  background-color: var(--color-bg);
}

.projects-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--spacing-lg);
}

.project-card {
  background-color: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--spacing-lg) var(--spacing-xl);
  box-shadow: var(--shadow-card);
  transition: transform var(--transition-base),
              box-shadow var(--transition-base),
              border-color var(--transition-base);
  cursor: default;
}

.project-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-card-hover);
  border-color: var(--color-accent-light);
}

.card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--spacing-md);
}

.card-tag {
  font-size: var(--text-xs);
  font-weight: var(--weight-semibold);
  color: var(--color-accent);
  background-color: var(--color-accent-light);
  padding: 3px var(--spacing-xs);
  border-radius: var(--radius-sm);
  letter-spacing: 0.04em;
}

.card-year {
  font-size: var(--text-xs);
  color: var(--color-text-muted);
  font-weight: var(--weight-medium);
}

.card-title {
  font-size: var(--text-lg);
  font-weight: var(--weight-semibold);
  color: var(--color-text-primary);
  margin-bottom: var(--spacing-sm);
  letter-spacing: -0.01em;
}

.card-desc {
  font-size: var(--text-sm);
  color: var(--color-text-secondary);
  line-height: 1.75;
  margin-bottom: var(--spacing-lg);
}

.card-tech {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-xs);
}

.card-tech span {
  font-size: var(--text-xs);
  font-weight: var(--weight-medium);
  color: var(--color-text-secondary);
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  padding: 2px var(--spacing-xs);
  border-radius: var(--radius-sm);
}

/* ============================
   Footer
   ============================ */
footer {
  background-color: var(--color-surface);
  border-top: 1px solid var(--color-border);
  padding: var(--spacing-xl) 0;
}

.footer-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: var(--spacing-md);
}

.footer-copy {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

.footer-email {
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  color: var(--color-accent);
  transition: opacity var(--transition-fast);
}

.footer-email:hover {
  opacity: 0.75;
  text-decoration: underline;
}

/* ============================
   페이드인 애니메이션
   ============================ */
.fade-in-up {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.55s ease, transform 0.55s ease;
}

.fade-in-up.visible {
  opacity: 1;
  transform: translateY(0);
}

/* Hero 섹션은 페이지 로드 시 즉시 보여야 하므로
   JS가 느릴 경우 대비하여 초기 opacity를 조정 */
#hero .fade-in-up {
  transition-delay: 0s;
}

/* ============================
   반응형 — 태블릿 (768px+)
   ============================ */
@media (min-width: 768px) {
  .projects-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

/* ============================
   반응형 — 데스크탑 (1024px+)
   ============================ */
@media (min-width: 1024px) {
  .projects-grid {
    grid-template-columns: repeat(3, 1fr);
  }
}

/* ============================
   반응형 — 모바일 (~767px)
   ============================ */
@media (max-width: 767px) {
  :root {
    --spacing-section: 4rem;
  }

  .container {
    padding: 0 var(--spacing-lg);
  }

  .nav-links {
    gap: var(--spacing-lg);
  }

  .hero-tagline {
    font-size: var(--text-base);
  }

  .timeline {
    padding-left: var(--spacing-lg);
  }

  .edu-header {
    flex-direction: column;
    gap: var(--spacing-xs);
  }

  .footer-inner {
    flex-direction: column;
    align-items: flex-start;
  }
}

/* ============================
   인쇄 스타일 (@media print)
   ============================ */
@media print {
  #nav { display: none; }

  body { color: #000; background: #fff; font-size: 11pt; }

  .btn { display: none; }

  #hero {
    min-height: unset;
    padding: 2rem 0;
  }

  .hero-name { font-size: 24pt; }
  .hero-tagline { font-size: 11pt; }

  .project-card,
  .timeline-content {
    box-shadow: none;
    border: 1px solid #ccc;
    break-inside: avoid;
  }

  .fade-in-up {
    opacity: 1 !important;
    transform: none !important;
  }

  footer { border-top: 1px solid #ccc; }
}