/* ===== Base Reset & Variables ===== */
:root {
  --imperial-blue: #003E74;
  --imperial-dark: #00294D;
  --black: #111111;
  --white: #ffffff;
  --off-white: #f7f8fa;
  --grey-light: #e4e7ec;
  --grey-mid: #6b7280;
  --grey-dark: #374151;
  --accent: #0060B6;
  --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  color: var(--black);
  background: var(--white);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--imperial-blue);
  text-decoration: none;
  transition: color var(--transition);
}

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

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

/* ===== Navigation ===== */
.navbar {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--black);
  border-bottom: 3px solid var(--imperial-blue);
  padding: 0 2rem;
}

.navbar-inner {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.navbar-brand {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--white);
  letter-spacing: -0.02em;
  transition: color var(--transition);
}

.navbar-brand:hover {
  color: var(--grey-light);
}

.navbar-links {
  list-style: none;
  display: flex;
  gap: 2rem;
}

.navbar-links a {
  color: rgba(255, 255, 255, 0.8);
  font-size: 0.9rem;
  font-weight: 500;
  letter-spacing: 0.03em;
  text-transform: uppercase;
  padding: 0.25rem 0;
  position: relative;
  transition: color var(--transition);
}

.navbar-links a::after {
  content: '';
  position: absolute;
  bottom: -4px;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--imperial-blue);
  transition: width var(--transition);
}

.navbar-links a:hover,
.navbar-links a.active {
  color: var(--white);
}

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

/* Mobile menu toggle */
.menu-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
}

.menu-toggle span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--white);
  margin: 5px 0;
  transition: var(--transition);
}

/* ===== Hero / Home Section ===== */
.hero {
  background: linear-gradient(135deg, var(--imperial-dark) 0%, var(--imperial-blue) 100%);
  color: var(--white);
  padding: 5rem 2rem;
}

.hero-inner {
  max-width: 1100px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 4rem;
  align-items: center;
}

.hero-photo {
  width: 280px;
  height: auto;
  border-radius: 6px;
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
}

.hero-text h1 {
  font-size: 2.75rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.15;
  margin-bottom: 0.75rem;
}

.hero-text .title {
  font-size: 1.15rem;
  color: rgba(255, 255, 255, 0.85);
  font-weight: 400;
  margin-bottom: 1.5rem;
  line-height: 1.5;
}

.hero-text .interests {
  font-size: 1rem;
  color: rgba(255, 255, 255, 0.7);
  line-height: 1.7;
  border-left: 3px solid rgba(255, 255, 255, 0.3);
  padding-left: 1.25rem;
  font-style: italic;
}

/* ===== Page Header ===== */
.page-header {
  background: linear-gradient(135deg, var(--imperial-dark) 0%, var(--imperial-blue) 100%);
  color: var(--white);
  padding: 3.5rem 2rem;
}

.page-header-inner {
  max-width: 1100px;
  margin: 0 auto;
}

.page-header h1 {
  font-size: 2.25rem;
  font-weight: 800;
  letter-spacing: -0.03em;
}

/* ===== Main Content ===== */
.content {
  max-width: 1100px;
  margin: 0 auto;
  padding: 3rem 2rem 5rem;
}

/* ===== Research Page ===== */
.research-category {
  margin-bottom: 3.5rem;
}

.research-category h2 {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--imperial-blue);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding-bottom: 0.75rem;
  border-bottom: 2px solid var(--imperial-blue);
  margin-bottom: 1.75rem;
}

.paper {
  padding: 1.25rem 0;
  border-bottom: 1px solid var(--grey-light);
}

.paper:last-child {
  border-bottom: none;
}

.paper-title {
  font-weight: 700;
  font-size: 1.05rem;
  color: var(--black);
  line-height: 1.4;
}

.paper-title a {
  color: var(--black);
  border-bottom: 1px solid transparent;
  transition: border-color var(--transition), color var(--transition);
}

.paper-title a:hover {
  color: var(--imperial-blue);
  border-bottom-color: var(--imperial-blue);
}

.paper-authors {
  color: var(--grey-dark);
  font-size: 0.95rem;
  margin-top: 0.3rem;
}

.paper-details {
  color: var(--grey-mid);
  font-size: 0.9rem;
  margin-top: 0.3rem;
}

.paper-links {
  margin-top: 0.5rem;
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
}

.paper-links a {
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--imperial-blue);
  padding: 0.25rem 0.7rem;
  border: 1px solid var(--imperial-blue);
  border-radius: 4px;
  transition: all var(--transition);
}

.paper-links a:hover {
  background: var(--imperial-blue);
  color: var(--white);
}

/* ===== Placeholder ===== */
.placeholder-text {
  font-size: 1.1rem;
  color: var(--grey-mid);
  text-align: center;
  padding: 4rem 0;
}

/* ===== Footer ===== */
.footer {
  background: var(--black);
  color: rgba(255, 255, 255, 0.5);
  text-align: center;
  padding: 2rem;
  font-size: 0.85rem;
}

.footer a {
  color: rgba(255, 255, 255, 0.7);
}

.footer a:hover {
  color: var(--white);
}

/* ===== Responsive ===== */
@media (max-width: 768px) {
  .hero-inner {
    grid-template-columns: 1fr;
    text-align: center;
    gap: 2rem;
  }

  .hero-photo {
    width: 200px;
    height: auto;
    margin: 0 auto;
  }

  .hero-text .interests {
    border-left: none;
    padding-left: 0;
    border-top: 2px solid rgba(255, 255, 255, 0.3);
    padding-top: 1rem;
  }

  .hero-text h1 {
    font-size: 2rem;
  }

  .menu-toggle {
    display: block;
  }

  .navbar-links {
    display: none;
    position: absolute;
    top: 64px;
    left: 0;
    right: 0;
    background: var(--black);
    flex-direction: column;
    padding: 1rem 2rem;
    gap: 1rem;
    border-bottom: 3px solid var(--imperial-blue);
  }

  .navbar-links.open {
    display: flex;
  }

  .navbar-links a::after {
    display: none;
  }

  .page-header h1 {
    font-size: 1.75rem;
  }
}