:root {
  --primary: #0f172a;
  --primary-light: #1e3a8a;
  --primary-accent: #1e40af;
  --secondary: #7c3aed;
  --bg: #ffffff;
  --bg-alt: #f8fafc;
  --bg-elevated: #ffffff;
  --text: #0f172a;
  --text-light: #475569;
  --text-muted: #64748b;
  --border: #cbd5e1;
  --border-strong: #94a3b8;
  --card-shadow: 0 1px 3px rgba(0,0,0,0.08);
  --card-shadow-hover: 0 8px 24px rgba(0,0,0,0.12);
  --hover-shadow: 0 4px 12px rgba(0,0,0,0.15);
  --gold: #d4af37;
  --gold-light: #f4e4bc;
}

@media (prefers-color-scheme: dark) {
  :root {
    --primary: #60a5fa;
    --primary-light: #93c5fd;
    --secondary: #a78bfa;
    --bg: #0f172a;
    --bg-alt: #1e293b;
    --bg-elevated: #1e293b;
    --text: #f1f5f9;
    --text-light: #94a3b8;
    --text-muted: #64748b;
    --border: #334155;
    --border-strong: #475569;
    --card-shadow: 0 1px 3px rgba(0,0,0,0.3);
    --card-shadow-hover: 0 8px 24px rgba(0,0,0,0.5);
    --hover-shadow: 0 4px 12px rgba(0,0,0,0.5);
  }
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px;
}

header {
  background: linear-gradient(135deg, var(--primary) 0%, var(--primary-accent) 100%);
  color: white;
  padding: 25px 0;
  border-bottom: 4px solid var(--gold);
  box-shadow: 0 4px 12px rgba(0,0,0,0.15);
  position: relative;
}

header::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: linear-gradient(90deg, transparent, var(--gold), transparent);
}

.header-content {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 15px;
}

.logo h1 {
  font-size: 2.25rem;
  font-weight: 700;
  margin-bottom: 5px;
  letter-spacing: -0.5px;
  text-shadow: 0 2px 4px rgba(0,0,0,0.2);
}

.logo p {
  opacity: 0.95;
  font-size: 0.9rem;
  font-weight: 400;
  letter-spacing: 0.5px;
  text-transform: uppercase;
}

.logo p a {
  text-decoration: none;
  color: white;
  transition: opacity 0.2s;
}

.logo p a:hover {
  opacity: 0.8;
}

.lang-switcher {
  display: flex;
  gap: 5px;
  background: rgba(255,255,255,0.1);
  padding: 4px;
  border-radius: 4px;
}

.lang-btn {
  background: transparent;
  border: 2px solid rgba(255,255,255,0.3);
  color: white;
  padding: 8px 16px;
  border-radius: 2px;
  cursor: pointer;
  font-size: 0.95rem;
  transition: background 0.2s, border-color 0.2s;
}

.lang-btn:hover {
  background: rgba(255,255,255,0.15);
  border-color: rgba(255,255,255,0.5);
}

.lang-btn.active {
  background: white;
  color: var(--primary);
  border-color: white;
}

nav {
  background: var(--bg-elevated);
  padding: 12px 0;
  border-bottom: 2px solid var(--border-strong);
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: 0 2px 8px rgba(0,0,0,0.08);
  backdrop-filter: blur(10px);
}

nav ul {
  list-style: none;
  display: flex;
  gap: 25px;
  flex-wrap: wrap;
}

nav a {
  color: var(--text);
  text-decoration: none;
  font-weight: 600;
  font-size: 0.95rem;
  transition: color 0.2s, border-color 0.2s;
  padding: 6px 0;
  border-bottom: 3px solid transparent;
  letter-spacing: 0.3px;
}

nav a:hover {
  color: var(--primary);
  border-bottom-color: var(--primary);
}

main {
  padding: 25px 0;
}

section {
  margin-bottom: 40px;
}

h2 {
  font-size: 2rem;
  margin-bottom: 15px;
  color: var(--primary);
  font-weight: 700;
  letter-spacing: -0.5px;
  border-bottom: 3px solid var(--primary);
  padding-bottom: 10px;
  display: inline-block;
  width: 100%;
}

h3 {
  font-size: 1.6rem;
  margin-bottom: 12px;
  margin-top: 25px;
  font-weight: 600;
  color: var(--primary);
  letter-spacing: -0.3px;
}

h4 {
  font-size: 1.2rem;
  margin-bottom: 8px;
  margin-top: 15px;
  font-weight: 600;
  color: var(--primary);
}

.intro {
  background: linear-gradient(to right, var(--bg-elevated) 0%, var(--bg-alt) 100%);
  padding: 25px;
  border-left: 5px solid var(--primary);
  margin-bottom: 25px;
  box-shadow: 0 4px 12px rgba(0,0,0,0.08);
  border-top: 1px solid var(--border);
  border-right: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}

.intro p {
  margin-bottom: 12px;
  font-size: 1.05rem;
  line-height: 1.7;
}

.intro strong {
  color: var(--primary);
  font-weight: 600;
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 15px;
  margin-top: 15px;
}

.card {
  background: var(--bg-elevated);
  padding: 20px;
  border: 2px solid var(--border);
  box-shadow: var(--card-shadow);
  transition: all 0.3s ease;
  position: relative;
  overflow: hidden;
}

.card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 4px;
  height: 100%;
  background: var(--primary);
  transform: scaleY(0);
  transition: transform 0.3s ease;
}

.card:hover {
  border-color: var(--primary);
  box-shadow: var(--card-shadow-hover);
  transform: translateY(-2px);
}

.card:hover::before {
  transform: scaleY(1);
}

.card h3 {
  margin-top: 0;
  color: var(--primary);
  font-weight: 700;
  font-size: 1.3rem;
  margin-bottom: 10px;
  letter-spacing: -0.3px;
}

.card ul {
  list-style: none;
  margin-top: 12px;
}

.card li {
  margin-bottom: 8px;
}

.card a {
  color: var(--text);
  text-decoration: none;
  transition: color 0.2s;
}

.card a:hover {
  color: var(--primary);
}

.card a.btn-secondary,
.btn-secondary {
  display: inline-block;
  padding: 8px 20px;
  background: transparent;
  color: var(--primary);
  border: 2px solid var(--primary);
  border-radius: 3px;
  font-weight: 600;
  text-decoration: none;
  transition: all 0.2s ease;
  letter-spacing: 0.3px;
  font-size: 0.95rem;
}

.card a.btn-secondary:hover,
.btn-secondary:hover {
  background: var(--primary);
  color: white;
  box-shadow: 0 4px 8px rgba(15, 23, 42, 0.2);
}

.year-details {
  margin: 10px 0;
  border: 2px solid var(--border);
  overflow: hidden;
}

.year-details summary {
  cursor: pointer;
  padding: 12px 18px;
  background: var(--bg-alt);
  font-weight: 600;
  font-size: 1.05rem;
  color: var(--primary);
  user-select: none;
  transition: background 0.2s;
}

.year-details summary:hover {
  background: var(--border);
}

.year-details[open] summary {
  border-bottom: 1px solid var(--border);
}

.file-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 8px;
  padding: 15px;
}

.file-grid a {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  background: var(--bg-alt);
  border-radius: 3px;
  text-decoration: none;
  color: var(--text);
  transition: background 0.2s, border-color 0.2s;
  border: 1px solid var(--border);
}

.file-grid a:hover {
  background: var(--border);
  border-color: var(--primary);
}

.file-grid a::before {
  content: "";
  display: inline-block;
  width: 22px;
  height: 22px;
  flex-shrink: 0;
  background-size: contain;
  background-repeat: no-repeat;
  background-position: center;
}

/* PDF Files */
.file-grid a[href$=".pdf"]::before,
.file-grid a[href$=".PDF"]::before {
  background-image: url('img/PDF_not_active.svg');
  transition: background-image 0.2s;
}

.file-grid a[href$=".pdf"]:hover::before,
.file-grid a[href$=".PDF"]:hover::before {
  background-image: url('img/PDF_active.svg');
}

/* Word Files */
.file-grid a[href$=".doc"]::before,
.file-grid a[href$=".docx"]::before,
.file-grid a[href$=".DOC"]::before,
.file-grid a[href$=".DOCX"]::before {
  background-image: url('img/word_inactive.svg');
  transition: background-image 0.2s;
}

.file-grid a[href$=".doc"]:hover::before,
.file-grid a[href$=".docx"]:hover::before,
.file-grid a[href$=".DOC"]:hover::before,
.file-grid a[href$=".DOCX"]:hover::before {
  background-image: url('img/word_active.svg');
}

/* Other file types keep PDF icon as fallback */
.file-grid a[href$=".jpg"]::before,
.file-grid a[href$=".JPG"]::before,
.file-grid a[href$=".png"]::before,
.file-grid a[href$=".PNG"]::before,
.file-grid a[href$=".rtf"]::before,
.file-grid a[href$=".txt"]::before,
.file-grid a[href$=".xlsx"]::before,
.file-grid a[href$=".ppt"]::before,
.file-grid a[href$=".ppsx"]::before,
.file-grid a[href$=".odt"]::before,
.file-grid a[href$=".nb"]::before,
.file-grid a[href$=".djvu"]::before {
  background-image: url('img/PDF_not_active.svg');
  transition: background-image 0.2s;
}

.file-grid a[href$=".jpg"]:hover::before,
.file-grid a[href$=".JPG"]:hover::before,
.file-grid a[href$=".png"]:hover::before,
.file-grid a[href$=".PNG"]:hover::before,
.file-grid a[href$=".rtf"]:hover::before,
.file-grid a[href$=".txt"]:hover::before,
.file-grid a[href$=".xlsx"]:hover::before,
.file-grid a[href$=".ppt"]:hover::before,
.file-grid a[href$=".ppsx"]:hover::before,
.file-grid a[href$=".odt"]:hover::before,
.file-grid a[href$=".nb"]:hover::before,
.file-grid a[href$=".djvu"]:hover::before {
  background-image: url('img/PDF_active.svg');
}

.nav-card {
  background: var(--bg-elevated);
  padding: 25px 20px;
  border-radius: 3px;
  text-decoration: none;
  color: var(--text);
  border: 2px solid var(--border);
  transition: all 0.3s ease;
  text-align: center;
  box-shadow: var(--card-shadow);
  position: relative;
  overflow: hidden;
}

.nav-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--primary);
  transform: scaleX(0);
  transition: transform 0.3s ease;
}

.nav-card:hover {
  border-color: var(--primary);
  box-shadow: var(--card-shadow-hover);
  transform: translateY(-3px);
}

.nav-card:hover::before {
  transform: scaleX(1);
}

.nav-card h4 {
  margin: 0;
  color: var(--primary);
  font-size: 1.3rem;
  font-weight: 700;
  letter-spacing: -0.3px;
  margin-bottom: 6px;
}

.nav-card small {
  color: var(--text-muted);
  font-weight: 500;
  font-size: 0.9rem;
  letter-spacing: 0.2px;
}

.btn {
  display: inline-block;
  padding: 10px 20px;
  background: var(--primary);
  color: white;
  text-decoration: none;
  border-radius: 3px;
  font-weight: 600;
  border: 2px solid var(--primary);
  transition: background 0.2s, border-color 0.2s;
}

.btn:hover {
  background: var(--primary-light);
  border-color: var(--primary-light);
}

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

.btn-secondary:hover {
  background: var(--primary);
  color: white;
}

footer {
  background: linear-gradient(135deg, var(--primary) 0%, var(--primary-accent) 100%);
  padding: 30px 0;
  margin-top: 50px;
  border-top: 4px solid var(--gold);
  text-align: center;
  color: white;
  font-size: 0.95rem;
  box-shadow: 0 -4px 12px rgba(0,0,0,0.1);
}

footer p {
  opacity: 0.95;
  font-weight: 400;
  letter-spacing: 0.3px;
}

/* Collapsible Sections */
details {
  margin: 10px 0;
  border: 2px solid var(--border);
}

summary {
  cursor: pointer;
  padding: 12px 18px;
  background: var(--bg-alt);
  font-weight: 600;
  font-size: 1.05rem;
  color: var(--primary);
  user-select: none;
  transition: background 0.2s;
}

summary:hover {
  background: var(--border);
}

details[open] summary {
  border-bottom: 1px solid var(--border);
}

body:not(.lang-ru) [lang="ru"],
body.lang-ru [lang="en"] {
  display: none !important;
}

@media (max-width: 768px) {
  .logo h1 {
    font-size: 1.8rem;
  }
  
  nav ul {
    gap: 15px;
  }
  
  .grid {
    grid-template-columns: 1fr;
  }
  
  .file-grid {
    grid-template-columns: 1fr;
  }
}