/* ============================================
   Vikas Yadav — Academic Research Portfolio
   Style System (clean, academic white theme)
   ============================================ */

/* ---------- CSS Custom Properties ---------- */
:root {
  --primary: #004AAD;
  --primary-light: #1a6fdd;
  --primary-dark: #003580;
  --accent: #ffc220;
  --bg: #fafbff;
  --bg-card: #ffffff;
  --text: #1a1a1a;
  --text-muted: #555;
  --text-light: #888;
  --border: #e2e8f0;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.08);
  --shadow-md: 0 4px 14px rgba(0,0,0,0.1);
  --shadow-lg: 0 10px 40px rgba(0,0,0,0.15);
  --radius: 12px;
  --radius-lg: 20px;
  --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --bg-alt: #f5f7fc;
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
}

/* ---------- Reset & Base ---------- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; font-size: 16px; }

body {
  font-family: var(--font-sans);
  background: #fff;
  color: var(--text);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--primary); text-decoration: none; transition: color var(--transition); }
a:hover { color: var(--primary-light); }
img { max-width: 100%; display: block; }

/* ---------- Typography ---------- */
h1, h2, h3, h4 { font-weight: 700; line-height: 1.3; }
h1 { font-size: clamp(2rem, 5vw, 3rem); }
h2 { font-size: clamp(1.5rem, 3vw, 2.2rem); }
h3 { font-size: 1.25rem; }

.section-title {
  text-align: center;
  margin-bottom: 1rem;
  color: var(--primary);
}

.section-subtitle {
  text-align: center;
  color: var(--text-muted);
  max-width: 700px;
  margin: 0 auto 3rem;
  font-size: 1.05rem;
}

/* ---------- Layout ---------- */
.container { max-width: 1200px; margin: 0 auto; padding: 0 1.5rem; }
section { padding: 4rem 0; }

/* ---------- Navigation ---------- */
.navbar {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 1000;
  background: rgba(255, 255, 255, 0.9);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
  transition: all var(--transition);
}

.navbar.scrolled { box-shadow: var(--shadow-sm); }

.navbar .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  height: 60px;
}

.nav-brand { font-weight: 800; font-size: 1.15rem; color: var(--primary); }

.nav-links { display: flex; gap: 1.75rem; list-style: none; }

.nav-links a {
  color: var(--text);
  font-weight: 500;
  font-size: 0.88rem;
  position: relative;
  padding: 0.25rem 0;
}

.nav-links a::after {
  content: '';
  position: absolute;
  bottom: -2px; left: 0;
  width: 0; height: 2px;
  background: var(--primary);
  transition: width var(--transition);
}

.nav-links a:hover::after,
.nav-links a.active::after { width: 100%; }

.nav-links .nav-cta {
  background: var(--primary);
  color: #fff !important;
  padding: 0.35rem 1rem;
  border-radius: 999px;
  transition: all var(--transition);
}

.nav-links .nav-cta:hover { background: var(--primary-dark); }
.nav-links .nav-cta::after { display: none !important; }

.nav-toggle {
  display: none;
  background: none; border: none; cursor: pointer; padding: 0.5rem;
}

.nav-toggle span {
  display: block; width: 22px; height: 2px;
  background: var(--text); margin: 5px 0;
  transition: var(--transition);
}

/* ---------- Hero (plain white, academic) ---------- */
.hero {
  background: #fff;
  padding: calc(60px + 3rem) 0 2.5rem;
  border-bottom: 1px solid var(--border);
}

.hero-content {
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: 2.5rem;
  align-items: start;
}

.hero-image {
  width: 200px;
  height: 200px;
  border-radius: 10px;
  border: 1px solid var(--border);
  overflow: hidden;
  background: #f8f9fa;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  flex-shrink: 0;
}

.hero-image img { width: 100%; height: 100%; object-fit: cover; }

.hero-image .placeholder-icon { width: 56px; height: 56px; opacity: 0.35; }

.hero-text h1 { color: var(--text); margin-bottom: 0.2rem; letter-spacing: -0.5px; }

.hero-role {
  color: var(--primary);
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: 0.75rem;
}

.hero-bio {
  color: var(--text-muted);
  font-size: 0.95rem;
  max-width: 640px;
  line-height: 1.75;
  margin-bottom: 0.75rem;
}

.hero-bio:last-of-type { margin-bottom: 1.25rem; }

.hero-bio strong { color: var(--text); }

/* ---------- Social Links ---------- */
.social-links { display: flex; gap: 0.5rem; flex-wrap: wrap; }

.social-link {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.4rem 0.85rem;
  background: #f1f5f9;
  border: 1px solid var(--border);
  border-radius: 999px;
  color: var(--text);
  font-size: 0.78rem;
  font-weight: 500;
  transition: all var(--transition);
}

.social-link:hover {
  background: var(--primary);
  color: #fff;
  border-color: var(--primary);
  transform: translateY(-1px);
}

.social-link svg { width: 14px; height: 14px; }

/* ---------- Section Alternating Background ---------- */
.section-alt { background: var(--bg-alt); }

/* ---------- Hero CTA ---------- */
.hero-cta {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  margin-top: 1.25rem;
  padding: 0.7rem 1.5rem;
  background: var(--primary);
  color: #fff;
  border-radius: 999px;
  font-size: 0.9rem;
  font-weight: 600;
  transition: all var(--transition);
}

.hero-cta:hover {
  background: var(--primary-dark);
  color: #fff;
  transform: translateY(-2px);
  box-shadow: 0 4px 16px rgba(0, 74, 173, 0.3);
}

.hero-cta svg { width: 18px; height: 18px; }

/* ---------- Recent News ---------- */
.news-list { list-style: none; padding: 0; margin: 0; }

.news-item {
  display: flex;
  gap: 1.25rem;
  padding: 1rem 0;
  border-bottom: 1px solid var(--border);
  align-items: baseline;
}

.news-item:last-child { border-bottom: none; }

.news-date {
  flex-shrink: 0;
  width: 90px;
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--primary);
  text-transform: uppercase;
  letter-spacing: 0.3px;
}

.news-body { font-size: 0.93rem; color: var(--text-muted); line-height: 1.6; }
.news-body a { color: var(--primary); }
.news-body a:hover { text-decoration: underline; }
.news-body strong { color: var(--text); }

/* ---------- Stats Bar ---------- */
.stats-bar { background: #fff; padding: 2rem 0; border-bottom: 1px solid var(--border); }

.stats-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 2rem;
  text-align: center;
}

.stat-item .stat-number {
  font-size: 2.5rem; font-weight: 800; color: var(--primary); line-height: 1;
}

.stat-item .stat-label {
  color: var(--text-muted); font-size: 0.85rem; font-weight: 500; margin-top: 0.25rem;
}

/* ---------- Research Cards ---------- */
.research-areas {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
}

.research-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  transition: all var(--transition);
  position: relative;
  overflow: hidden;
}

.research-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 4px;
  background: var(--primary);
  transform: scaleX(0);
  transition: transform var(--transition);
}

.research-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-lg); }
.research-card:hover::before { transform: scaleX(1); }

.research-card-icon {
  width: 48px; height: 48px;
  background: rgba(0, 74, 173, 0.08);
  border-radius: 12px;
  display: flex; align-items: center; justify-content: center;
  margin-bottom: 1rem;
}

.research-card-icon svg { width: 24px; height: 24px; color: var(--primary); }
.research-card h3 { margin-bottom: 0.5rem; color: var(--text); }
.research-card p { color: var(--text-muted); font-size: 0.9rem; }

/* ---------- Papers Section ---------- */
.papers-controls {
  display: flex; justify-content: center;
  gap: 0.5rem; margin-bottom: 2rem; flex-wrap: wrap;
}

.filter-btn {
  padding: 0.5rem 1.25rem;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: var(--bg-card);
  color: var(--text-muted);
  font-size: 0.85rem; font-weight: 500;
  cursor: pointer;
  transition: all var(--transition);
}

.filter-btn:hover,
.filter-btn.active {
  background: var(--primary); color: #fff; border-color: var(--primary);
}

/* ---------- Paper Cards ---------- */
.papers-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(360px, 1fr));
  gap: 1.5rem;
}

.paper-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: all var(--transition);
  cursor: pointer;
}

.paper-card:hover { transform: translateY(-6px); box-shadow: var(--shadow-lg); }

.paper-card-image { width: 100%; height: 200px; position: relative; overflow: hidden; background: var(--bg-alt); }
.paper-card-image img { width: 100%; height: 100%; object-fit: contain; background: var(--bg-alt); }
.paper-card-image svg { width: 100%; height: 100%; }

.paper-venue-badge {
  position: absolute;
  top: 12px; right: 12px;
  background: var(--primary); color: #fff;
  padding: 0.25rem 0.75rem;
  border-radius: 999px;
  font-size: 0.72rem; font-weight: 700;
  letter-spacing: 0.5px;
  text-transform: uppercase;
  box-shadow: 0 2px 8px rgba(0,0,0,0.2);
}

.paper-card-body { padding: 1.5rem; }

.paper-date {
  color: var(--primary);
  font-size: 0.78rem; font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 0.5rem;
}

.paper-card-body h3 {
  font-size: 1.05rem; line-height: 1.4;
  margin-bottom: 0.75rem; color: var(--text);
  transition: color var(--transition);
}

.paper-card:hover .paper-card-body h3 { color: var(--primary); }

.paper-abstract {
  color: var(--text-muted);
  font-size: 0.88rem; line-height: 1.6;
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.paper-card-footer {
  padding: 0 1.5rem 1.5rem;
  display: flex; justify-content: space-between; align-items: center;
}

.paper-link {
  display: inline-flex; align-items: center; gap: 0.35rem;
  font-size: 0.82rem; font-weight: 600; color: var(--primary);
}

.paper-link:hover { color: var(--primary-dark); }
.paper-link svg { width: 14px; height: 14px; }

/* ---------- Paper Modal ---------- */
.modal-overlay {
  display: none;
  position: fixed;
  top: 0; left: 0; right: 0; bottom: 0;
  background: rgba(0, 0, 0, 0.6);
  backdrop-filter: blur(4px);
  z-index: 2000;
  align-items: center; justify-content: center;
  padding: 2rem;
}

.modal-overlay.active { display: flex; }

.modal {
  background: #fff;
  border-radius: var(--radius-lg);
  max-width: 700px; width: 100%;
  max-height: 85vh;
  overflow-y: auto;
  position: relative;
  animation: modalIn 0.3s ease;
}

@keyframes modalIn {
  from { opacity: 0; transform: scale(0.95) translateY(20px); }
  to { opacity: 1; transform: scale(1) translateY(0); }
}

.modal-close {
  position: absolute; top: 1rem; right: 1rem;
  width: 36px; height: 36px;
  border: none; background: rgba(0,0,0,0.05);
  border-radius: 50%; cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  z-index: 1; transition: background var(--transition);
}

.modal-close:hover { background: rgba(0,0,0,0.1); }

.modal-image {
  width: 100%; height: 280px;
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
  overflow: hidden;
}

.modal-image svg { width: 100%; height: 100%; }
.modal-body { padding: 2rem; }
.modal-body h2 { font-size: 1.4rem; margin-bottom: 0.75rem; color: var(--text); }

.modal-meta { display: flex; gap: 1rem; margin-bottom: 1.5rem; flex-wrap: wrap; }

.modal-meta span {
  font-size: 0.82rem; padding: 0.3rem 0.8rem;
  background: rgba(0, 74, 173, 0.06);
  border-radius: 999px; color: var(--primary); font-weight: 600;
}

.modal-body .abstract-full {
  color: var(--text-muted); font-size: 0.95rem;
  line-height: 1.8; margin-bottom: 1.5rem;
}

.modal-cta {
  display: inline-flex; align-items: center; gap: 0.5rem;
  padding: 0.75rem 1.5rem;
  background: var(--primary); color: #fff;
  border-radius: 999px; font-weight: 600; font-size: 0.9rem;
  transition: all var(--transition);
}

.modal-cta:hover {
  background: var(--primary-dark); color: #fff;
  transform: translateY(-2px);
  box-shadow: 0 4px 16px rgba(0, 74, 173, 0.3);
}

/* ---------- Contact Form ---------- */
.contact-form {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: var(--shadow-sm);
}

.form-group { margin-bottom: 1.25rem; text-align: left; }

.form-group label {
  display: block; font-size: 0.85rem;
  font-weight: 600; color: var(--text); margin-bottom: 0.4rem;
}

.form-group input,
.form-group textarea {
  width: 100%; padding: 0.75rem 1rem;
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  font-family: var(--font-sans);
  font-size: 0.95rem; color: var(--text);
  background: #fff;
  transition: border-color var(--transition), box-shadow var(--transition);
  outline: none;
}

.form-group input:focus,
.form-group textarea:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(0, 74, 173, 0.1);
}

.form-group input::placeholder,
.form-group textarea::placeholder { color: var(--text-light); }

.form-group textarea { resize: vertical; min-height: 100px; }

.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}

.form-submit {
  display: inline-flex; align-items: center; gap: 0.5rem;
  padding: 0.85rem 2rem;
  background: var(--primary); color: #fff;
  border: none; border-radius: 999px;
  font-family: var(--font-sans);
  font-size: 0.95rem; font-weight: 600;
  cursor: pointer; transition: all var(--transition);
  margin-top: 0.5rem;
}

.form-submit:hover {
  background: var(--primary-dark);
  transform: translateY(-2px);
  box-shadow: 0 4px 16px rgba(0, 74, 173, 0.3);
}

.form-submit:active { transform: translateY(0); }
.form-submit:disabled { opacity: 0.6; cursor: not-allowed; transform: none; }
.form-submit .btn-icon { transition: transform var(--transition); }
.form-submit:hover .btn-icon { transform: translateX(3px); }

.form-status {
  margin-top: 1.5rem; padding: 1rem 1.5rem;
  border-radius: var(--radius);
  font-size: 0.9rem; font-weight: 500; text-align: center;
}

.form-status.success {
  background: rgba(42, 135, 3, 0.08); color: #2a8703;
  border: 1px solid rgba(42, 135, 3, 0.2);
}

.form-status.error {
  background: rgba(234, 17, 0, 0.08); color: #ea1100;
  border: 1px solid rgba(234, 17, 0, 0.2);
}

/* ---------- Footer ---------- */
.footer {
  background: #0a0a2e;
  color: rgba(255, 255, 255, 0.7);
  padding: 3rem 0 2rem;
  text-align: center;
}

.footer a { color: var(--accent); }
.footer a:hover { color: #fff; }

.footer-links {
  display: flex; justify-content: center;
  gap: 2rem; margin-bottom: 1.5rem;
}

.footer-text { font-size: 0.85rem; opacity: 0.6; }

/* ---------- Scroll Animations ---------- */
.fade-in {
  opacity: 0; transform: translateY(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

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

/* ---------- Responsive ---------- */
@media (max-width: 768px) {
  .hero-content {
    grid-template-columns: 1fr;
    text-align: center; gap: 1.5rem;
  }

  .hero-image { width: 150px; height: 150px; margin: 0 auto; }
  .social-links { justify-content: center; }
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .papers-grid { grid-template-columns: 1fr; }

  .news-item { flex-direction: column; gap: 0.25rem; }
  .news-date { width: auto; }

  .nav-links { display: none; }
  .nav-links.open {
    display: flex; flex-direction: column;
    position: absolute; top: 60px; left: 0; right: 0;
    background: #fff; padding: 1rem;
    border-bottom: 1px solid var(--border);
    box-shadow: var(--shadow-md);
  }

  .nav-toggle { display: block; }
}

@media (max-width: 480px) {
  section { padding: 3rem 0; }
  .stats-grid { grid-template-columns: 1fr 1fr; gap: 1rem; }
  .form-row { grid-template-columns: 1fr; }
}