/* Design System: Dark Mode Premium */
:root {
  --bg-primary: #0A0A0B;
  --bg-secondary: #1F2937;
  --text-primary: #E5E7EB;
  --text-secondary: #9CA3AF;
  --accent: #22D3EE;
  --border-color: rgba(255, 255, 255, 0.08);
  
  --font-en: 'Inter', sans-serif;
  --font-kr: 'Pretendard', 'Noto Sans KR', sans-serif;
  
  --shadow-float: 0 12px 32px rgba(0, 0, 0, 0.4);
  --shadow-hover: 0 16px 48px rgba(0, 0, 0, 0.6);
  --radius-card: 16px;
  --radius-btn: 8px;
  
  --transition-slow: 0.6s cubic-bezier(0.16, 1, 0.3, 1);
  --transition-normal: 0.3s ease;
  
  --max-width: 1200px;
  --spacing-section: 120px;
}

/* Base Styles */
* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-en); /* Default to EN, JS will toggle class based on lang */
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

body.lang-kr {
  font-family: var(--font-kr);
}

body.lang-kr .en-only { display: none !important; }
body.lang-en .kr-only { display: none !important; }

h1, h2, h3, h4, h5, h6 {
  font-weight: 400;
  line-height: 1.2;
  letter-spacing: -0.02em;
}

h1 { font-size: 3.5rem; }
h2 { font-size: 2.5rem; margin-bottom: 2rem; }
h3 { font-size: 1.5rem; margin-bottom: 1rem; }

a {
  color: inherit;
  text-decoration: none;
  transition: color var(--transition-normal);
}

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

ul {
  list-style: none;
}

.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 2rem;
}

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

/* Typography elements */
.text-accent { color: var(--accent); }
.text-secondary { color: var(--text-secondary); }

/* Buttons */
.btn {
  display: inline-block;
  padding: 12px 24px;
  border-radius: var(--radius-btn);
  font-weight: 500;
  font-size: 1rem;
  cursor: pointer;
  transition: all var(--transition-normal);
  text-align: center;
  border: 1px solid transparent;
}

.btn-primary {
  background-color: var(--text-primary);
  color: var(--bg-primary);
}

.btn-primary:hover {
  background-color: var(--accent);
  color: var(--bg-primary);
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(34, 211, 238, 0.2);
}

.btn-secondary {
  background-color: transparent;
  color: var(--text-primary);
  border-color: var(--border-color);
}

.btn-secondary:hover {
  background-color: var(--bg-secondary);
  border-color: var(--text-secondary);
  transform: translateY(-2px);
}

.btn-sm {
  padding: 8px 16px;
  font-size: 0.875rem;
}

/* Header & Nav */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  z-index: 1000;
  background: rgba(10, 10, 11, 0.85);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-color);
}

.header-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  height: 80px;
}

.logo a {
  font-size: 1.25rem;
  font-weight: 600;
  letter-spacing: -0.01em;
  color: var(--text-primary);
}

.main-nav .nav-links {
  display: flex;
  align-items: center;
  gap: 2rem;
}

.main-nav a {
  font-size: 0.9rem;
  color: var(--text-secondary);
}

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

.dropdown {
  position: relative;
}

.dropdown-trigger {
  font-size: 0.9rem;
  color: var(--text-secondary);
  cursor: pointer;
  transition: color var(--transition-normal);
}

.dropdown-menu {
  position: absolute;
  top: 100%;
  left: 50%;
  transform: translateX(-50%) translateY(10px);
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-btn);
  padding: 1rem;
  min-width: 260px;
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition-normal);
  box-shadow: var(--shadow-float);
}

.dropdown:hover .dropdown-menu {
  opacity: 1;
  visibility: visible;
  transform: translateX(-50%) translateY(0);
}

.dropdown-menu li {
  margin-bottom: 0.5rem;
}

.dropdown-menu li:last-child {
  margin-bottom: 0;
}

.dropdown-menu a {
  display: block;
  padding: 0.5rem;
  border-radius: 4px;
}

.dropdown-menu a:hover {
  background-color: rgba(255, 255, 255, 0.05);
  color: var(--accent);
}

.lang-switch {
  display: flex;
  align-items: center;
}

.btn-lang {
  background: none;
  border: none;
  color: var(--text-secondary);
  font-size: 0.85rem;
  cursor: pointer;
  padding: 4px 8px;
  transition: color var(--transition-normal);
}

.btn-lang span.active {
  color: var(--text-primary);
  font-weight: 600;
}

/* Animations */
.fade-in {
  opacity: 0;
  transform: translateY(20px);
  animation: fadeInUp var(--transition-slow) forwards;
}

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

.delay-1 { animation-delay: 0.1s; }
.delay-2 { animation-delay: 0.2s; }
.delay-3 { animation-delay: 0.3s; }

/* Components */
.card {
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-card);
  padding: 2.5rem;
  box-shadow: var(--shadow-float);
  transition: transform var(--transition-slow), box-shadow var(--transition-slow);
}

.card:hover {
  transform: translateY(-8px);
  box-shadow: var(--shadow-hover);
}

/* Main Content Area */
main#app {
  min-height: calc(100vh - 80px); /* fallback */
}

/* Footer */
.site-footer {
  background-color: #050505;
  border-top: 1px solid var(--border-color);
  padding: 4rem 0 2rem;
  margin-top: 4rem;
}

.footer-inner {
  display: flex;
  justify-content: space-between;
  margin-bottom: 3rem;
  flex-wrap: wrap;
  gap: 2rem;
}

.footer-brand h3 {
  font-size: 1.25rem;
  margin-bottom: 0.5rem;
}

.footer-brand p {
  color: var(--text-secondary);
  max-width: 300px;
}

.footer-links {
  display: flex;
  gap: 4rem;
}

.footer-col h4 {
  font-size: 1rem;
  margin-bottom: 1rem;
  color: var(--text-primary);
}

.footer-col ul li {
  margin-bottom: 0.75rem;
  color: var(--text-secondary);
  font-size: 0.9rem;
}

.footer-bottom {
  border-top: 1px solid var(--border-color);
  padding-top: 2rem;
  text-align: center;
  color: var(--text-secondary);
  font-size: 0.85rem;
}

/* Utilities */
.text-center { text-align: center; }
.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem; }
.mb-3 { margin-bottom: 1.5rem; }
.mb-4 { margin-bottom: 2rem; }
.mb-5 { margin-bottom: 3rem; }
.mt-5 { margin-top: 3rem; }

/* Responsive Grid */
.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 2rem;
}

.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 2rem;
}

@media (max-width: 992px) {
  .grid-3 { grid-template-columns: repeat(2, 1fr); }
  h1 { font-size: 2.8rem; }
}

@media (max-width: 768px) {
  .header-inner { height: auto; padding: 1rem 0; flex-direction: column; gap: 1rem; }
  .main-nav .nav-links { flex-wrap: wrap; justify-content: center; gap: 1rem; }
  .grid-2, .grid-3 { grid-template-columns: 1fr; }
  h1 { font-size: 2.2rem; }
  .footer-links { flex-direction: column; gap: 2rem; }
}