/* ===========================
   CSS Custom Properties
   =========================== */
:root {
  /* Light theme (default) */
  --color-bg: #fafafa;
  --color-bg-alt: #ffffff;
  --color-text: #1a1a2e;
  --color-text-secondary: #555;
  --color-accent: #4361ee;
  --color-accent-light: rgba(67, 97, 238, 0.1);
  --color-border: #e0e0e0;
  --color-card-bg: #ffffff;
  --color-card-shadow: rgba(0, 0, 0, 0.08);
  --color-tag-bg: #f0f0f5;
  --color-tag-text: #4361ee;
  --color-nav-bg: rgba(250, 250, 250, 0.9);
  --color-footer-bg: #1a1a2e;
  --color-footer-text: #ccc;

  /* Spacing */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 2rem;
  --space-xl: 4rem;
  --space-2xl: 6rem;

  /* Typography */
  --font-sans: 'Pretendard', 'Apple SD Gothic Neo', 'Malgun Gothic', 'Noto Sans KR', sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', 'Consolas', monospace;

  /* Layout */
  --max-width: 1100px;
  --nav-height: 60px;
  --border-radius: 12px;

  /* Transition */
  --transition-fast: 0.2s ease;
  --transition-base: 0.3s ease;
}

[data-theme="dark"] {
  --color-bg: #0f0f1a;
  --color-bg-alt: #1a1a2e;
  --color-text: #e0e0e0;
  --color-text-secondary: #999;
  --color-accent: #6c8cff;
  --color-accent-light: rgba(108, 140, 255, 0.15);
  --color-border: #2a2a3e;
  --color-card-bg: #1e1e32;
  --color-card-shadow: rgba(0, 0, 0, 0.3);
  --color-tag-bg: rgba(108, 140, 255, 0.15);
  --color-tag-text: #8ca8ff;
  --color-nav-bg: rgba(15, 15, 26, 0.9);
  --color-footer-bg: #0a0a14;
  --color-footer-text: #888;
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  background-color: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  transition: background-color var(--transition-base), color var(--transition-base);
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--color-accent);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--color-text);
}

/* ===========================
   Navigation
   =========================== */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  height: var(--nav-height);
  background: var(--color-nav-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid transparent;
  transition: border-color var(--transition-base), background-color var(--transition-base);
}

.nav--scrolled {
  border-bottom-color: var(--color-border);
}

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

.nav__logo {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--color-text);
  letter-spacing: -0.02em;
}

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

.nav__links {
  display: flex;
  align-items: center;
  gap: var(--space-lg);
}

.nav__link {
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--color-text-secondary);
}

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

/* Theme Toggle */
.theme-toggle {
  background: none;
  border: 1px solid var(--color-border);
  border-radius: 8px;
  padding: 6px;
  cursor: pointer;
  color: var(--color-text);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: border-color var(--transition-fast), color var(--transition-fast);
}

.theme-toggle:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
}

.theme-toggle__icon--moon {
  display: none;
}

[data-theme="dark"] .theme-toggle__icon--sun {
  display: none;
}

[data-theme="dark"] .theme-toggle__icon--moon {
  display: block;
}

/* ===========================
   Hero
   =========================== */
.hero {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: var(--space-lg);
  position: relative;
}

.hero__greeting {
  font-size: clamp(1rem, 2vw, 1.25rem);
  color: var(--color-text-secondary);
  margin-bottom: var(--space-sm);
}

.hero__name {
  font-size: clamp(2.5rem, 8vw, 5rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.1;
  margin-bottom: var(--space-md);
  background: linear-gradient(135deg, var(--color-accent), #7b68ee);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero__tagline {
  font-size: clamp(1rem, 2.5vw, 1.3rem);
  color: var(--color-text-secondary);
  max-width: 500px;
  margin-bottom: var(--space-xl);
}

.hero__cta {
  display: inline-block;
  padding: 0.8rem 2rem;
  background: var(--color-accent);
  color: #fff;
  border-radius: 50px;
  font-weight: 600;
  font-size: 1rem;
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

.hero__cta:hover {
  color: #fff;
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(67, 97, 238, 0.3);
}

.hero__scroll-arrow {
  position: absolute;
  bottom: 2rem;
  color: var(--color-text-secondary);
  animation: bounce 2s ease infinite;
}

@keyframes bounce {
  0%, 20%, 50%, 80%, 100% { transform: translateY(0); }
  40% { transform: translateY(-12px); }
  60% { transform: translateY(-6px); }
}

/* ===========================
   Section Title
   =========================== */
.section-title {
  text-align: center;
  font-size: clamp(1.5rem, 4vw, 2.2rem);
  font-weight: 700;
  margin-bottom: var(--space-2xl);
  letter-spacing: -0.02em;
}

/* ===========================
   Timeline
   =========================== */
.timeline-section {
  padding: var(--space-2xl) var(--space-lg);
  max-width: var(--max-width);
  margin: 0 auto;
}

.timeline {
  position: relative;
  padding: var(--space-lg) 0;
}

/* Center line */
.timeline__line {
  position: absolute;
  left: 50%;
  top: 0;
  bottom: 0;
  width: 2px;
  background: var(--color-border);
  transform: translateX(-50%);
}

.timeline__progress {
  width: 100%;
  height: 0%;
  background: var(--color-accent);
  transition: height 0.1s linear;
  border-radius: 1px;
}

/* Timeline item */
.timeline__item {
  position: relative;
  width: 50%;
  padding: 0 var(--space-xl) var(--space-2xl);
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.timeline__item.is-visible {
  opacity: 1;
  transform: translateY(0);
}

.timeline__item--left {
  padding-right: var(--space-xl);
  text-align: right;
}

.timeline__item--right {
  margin-left: 50%;
  padding-left: var(--space-xl);
  text-align: left;
}

/* Dot marker */
.timeline__dot {
  position: absolute;
  top: 6px;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--color-bg);
  border: 3px solid var(--color-accent);
  z-index: 2;
  transition: background-color var(--transition-base);
}

.timeline__item--left .timeline__dot {
  right: -8px;
}

.timeline__item--right .timeline__dot {
  left: -8px;
}

.timeline__dot--pulse {
  animation: pulse 2s ease infinite;
  background: var(--color-accent);
}

@keyframes pulse {
  0% { box-shadow: 0 0 0 0 rgba(67, 97, 238, 0.5); }
  70% { box-shadow: 0 0 0 12px rgba(67, 97, 238, 0); }
  100% { box-shadow: 0 0 0 0 rgba(67, 97, 238, 0); }
}

/* Card */
.timeline__card {
  background: var(--color-card-bg);
  border-radius: var(--border-radius);
  padding: var(--space-lg);
  box-shadow: 0 4px 16px var(--color-card-shadow);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast), background-color var(--transition-base);
  position: relative;
}

.timeline__card:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 32px var(--color-card-shadow);
}

.timeline__number {
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--color-accent);
  font-family: var(--font-mono);
  letter-spacing: 0.05em;
}

.timeline__badge {
  display: inline-block;
  padding: 2px 10px;
  background: var(--color-accent);
  color: #fff;
  border-radius: 50px;
  font-size: 0.7rem;
  font-weight: 600;
  margin-left: var(--space-sm);
  vertical-align: middle;
}

.timeline__company {
  font-size: 1.3rem;
  font-weight: 700;
  margin: var(--space-sm) 0;
  letter-spacing: -0.01em;
}

.timeline__company-en {
  font-size: 0.85rem;
  font-weight: 400;
  color: var(--color-text-secondary);
}

.timeline__period {
  font-size: 0.85rem;
  color: var(--color-text-secondary);
  font-family: var(--font-mono);
  margin-bottom: var(--space-xs);
}

.timeline__role {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--color-accent);
  margin-bottom: var(--space-md);
}

.timeline__desc {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  line-height: 1.7;
  margin-bottom: var(--space-md);
}

/* Tags */
.timeline__tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
}

.timeline__item--left .timeline__tags {
  justify-content: flex-end;
}

.tag {
  display: inline-block;
  padding: 4px 12px;
  background: var(--color-tag-bg);
  color: var(--color-tag-text);
  border-radius: 50px;
  font-size: 0.75rem;
  font-weight: 500;
  transition: background-color var(--transition-base), color var(--transition-base);
}

/* ===========================
   Footer
   =========================== */
.footer {
  background: var(--color-footer-bg);
  color: var(--color-footer-text);
  padding: var(--space-2xl) var(--space-lg);
  text-align: center;
  transition: background-color var(--transition-base);
}

.footer__inner {
  max-width: var(--max-width);
  margin: 0 auto;
}

.footer__title {
  font-size: 1.5rem;
  font-weight: 700;
  color: #fff;
  margin-bottom: var(--space-lg);
}

.footer__links {
  display: flex;
  justify-content: center;
  gap: var(--space-xl);
  margin-bottom: var(--space-lg);
  flex-wrap: wrap;
}

.footer__link {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  color: var(--color-footer-text);
  font-size: 0.95rem;
  transition: color var(--transition-fast);
}

.footer__link:hover {
  color: #fff;
}

.footer__copy {
  font-size: 0.8rem;
  color: var(--color-footer-text);
  opacity: 0.6;
}

/* ===========================
   Responsive (Mobile)
   =========================== */
@media (max-width: 768px) {
  .timeline__line {
    left: 20px;
  }

  .timeline__item {
    width: 100%;
    padding-left: 50px;
    padding-right: var(--space-md);
    text-align: left;
  }

  .timeline__item--left {
    text-align: left;
    padding-right: var(--space-md);
  }

  .timeline__item--right {
    margin-left: 0;
    padding-left: 50px;
  }

  .timeline__item--left .timeline__dot,
  .timeline__item--right .timeline__dot {
    left: 12px;
    right: auto;
  }

  .timeline__item--left .timeline__tags {
    justify-content: flex-start;
  }

  .hero__name {
    font-size: clamp(2rem, 10vw, 3.5rem);
  }

  .footer__links {
    flex-direction: column;
    align-items: center;
    gap: var(--space-md);
  }
}

/* ===========================
   Accessibility
   =========================== */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }

  html {
    scroll-behavior: auto;
  }

  .timeline__item {
    opacity: 1;
    transform: none;
  }
}