/* ==========================================================================
   Christoph Gerhardt — Academic Personal Page
   Clean, modern, responsive CSS
   ========================================================================== */

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

:root {
  --color-primary:    #1a56db;
  --color-primary-dk: #143faa;
  --color-accent:     #2563eb;
  --color-bg:         #f8fafc;
  --color-card:       #ffffff;
  --color-text:       #1e293b;
  --color-text-muted: #64748b;
  --color-border:     #e2e8f0;
  --color-tag-bg:     #eff6ff;
  --color-tag-text:   #1d4ed8;
  --font-sans:        'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono:        'JetBrains Mono', 'Fira Code', monospace;
  --shadow-sm:        0 1px 2px rgba(0,0,0,.05);
  --shadow-md:        0 4px 12px rgba(0,0,0,.08);
  --shadow-lg:        0 10px 30px rgba(0,0,0,.10);
  --radius:           8px;
  --max-width:        960px;
  --transition:       .25s ease;
}

html { scroll-behavior: smooth; }

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.7;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--color-primary); text-decoration: none; transition: color var(--transition); }
a:hover { color: var(--color-primary-dk); text-decoration: underline; }

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

/* --- Navigation ----------------------------------------------------------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255,255,255,.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
}

.nav__inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: .75rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav__brand {
  font-weight: 700;
  font-size: 1.1rem;
  color: var(--color-text);
  letter-spacing: -.02em;
}
.nav__brand:hover { color: var(--color-primary); text-decoration: none; }

.nav__links { display: flex; gap: 1.5rem; list-style: none; }
.nav__links a {
  font-size: .9rem;
  font-weight: 500;
  color: var(--color-text-muted);
  transition: color var(--transition);
}
.nav__links a:hover,
.nav__links a.active { color: var(--color-primary); text-decoration: none; }

/* Hamburger */
.nav__toggle { display: none; background: none; border: none; cursor: pointer; padding: 4px; }
.nav__toggle svg { width: 24px; height: 24px; stroke: var(--color-text); }

/* --- Hero / Header -------------------------------------------------------- */
.hero {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 3rem 1.5rem 2rem;
  display: flex;
  align-items: center;
  gap: 2.5rem;
}

.hero__photo {
  width: 160px;
  height: 160px;
  border-radius: 50%;
  object-fit: cover;
  border: 4px solid var(--color-card);
  box-shadow: var(--shadow-md);
  flex-shrink: 0;
}

.hero__info h1 {
  font-size: 2rem;
  font-weight: 800;
  letter-spacing: -.03em;
  line-height: 1.2;
}

.hero__info .subtitle {
  font-size: 1.1rem;
  color: var(--color-text-muted);
  margin-top: .35rem;
}

.hero__links {
  display: flex;
  flex-wrap: wrap;
  gap: .6rem;
  margin-top: 1rem;
  list-style: none;
}

.hero__links a {
  display: inline-flex;
  align-items: center;
  gap: .35rem;
  padding: .35rem .75rem;
  background: var(--color-tag-bg);
  color: var(--color-tag-text);
  border-radius: 999px;
  font-size: .85rem;
  font-weight: 500;
  transition: background var(--transition), color var(--transition);
}
.hero__links a:hover {
  background: var(--color-primary);
  color: #fff;
  text-decoration: none;
}

/* --- Main Content --------------------------------------------------------- */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.5rem 3rem;
}

/* --- Section -------------------------------------------------------------- */
.section { margin-bottom: 2.5rem; }

.section__title {
  font-size: 1.35rem;
  font-weight: 700;
  letter-spacing: -.02em;
  margin-bottom: 1rem;
  padding-bottom: .5rem;
  border-bottom: 2px solid var(--color-primary);
  display: inline-block;
}

.section__subtitle {
  font-size: 1.05rem;
  font-weight: 600;
  margin: 1.5rem 0 .75rem;
  color: var(--color-text);
}

/* --- Cards ---------------------------------------------------------------- */
.card {
  background: var(--color-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin-bottom: 1rem;
  box-shadow: var(--shadow-sm);
  transition: box-shadow var(--transition), transform var(--transition);
}
.card:hover { box-shadow: var(--shadow-md); transform: translateY(-1px); }

.card__header {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  flex-wrap: wrap;
  gap: .5rem;
}

.card__title {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--color-text);
}

.card__meta {
  font-size: .85rem;
  color: var(--color-text-muted);
  font-weight: 500;
}

.card__org {
  font-size: .95rem;
  color: var(--color-text-muted);
  margin-top: .15rem;
}

.card__desc {
  margin-top: .5rem;
  font-size: .93rem;
  color: var(--color-text);
  line-height: 1.65;
}

.card__desc ul { margin-top: .4rem; padding-left: 1.2rem; }
.card__desc li { margin-bottom: .2rem; }

/* --- Tags ----------------------------------------------------------------- */
.tags { display: flex; flex-wrap: wrap; gap: .4rem; margin-top: .75rem; }

.tag {
  display: inline-block;
  padding: .2rem .65rem;
  background: var(--color-tag-bg);
  color: var(--color-tag-text);
  border-radius: 999px;
  font-size: .78rem;
  font-weight: 500;
}

/* --- Publication List ----------------------------------------------------- */
.pub-list { list-style: none; counter-reset: pub; }

.pub-item {
  position: relative;
  padding: 1rem 1.25rem 1rem 3.25rem;
  background: var(--color-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  margin-bottom: .75rem;
  box-shadow: var(--shadow-sm);
  font-size: .93rem;
  line-height: 1.6;
  transition: box-shadow var(--transition);
}
.pub-item:hover { box-shadow: var(--shadow-md); }

.pub-item::before {
  counter-increment: pub;
  content: "[" counter(pub) "]";
  position: absolute;
  left: 1rem;
  top: 1rem;
  font-weight: 700;
  color: var(--color-primary);
  font-size: .85rem;
}

.pub-item .authors { color: var(--color-text-muted); }
.pub-item .authors strong { color: var(--color-text); font-weight: 600; }
.pub-item .title { font-weight: 600; }
.pub-item .venue { font-style: italic; }
.pub-item .doi { font-family: var(--font-mono); font-size: .8rem; }

.pub-item .pub-badge {
  display: inline-block;
  padding: .1rem .5rem;
  border-radius: 999px;
  font-size: .72rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: .04em;
  margin-left: .5rem;
  vertical-align: middle;
}
.pub-badge--first  { background: #dbeafe; color: #1e40af; }
.pub-badge--review { background: #fef3c7; color: #92400e; }

/* --- Skills Grid ---------------------------------------------------------- */
.skills-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1rem;
}

.skill-card {
  background: var(--color-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1rem 1.25rem;
  box-shadow: var(--shadow-sm);
}

.skill-card__title {
  font-size: .85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .05em;
  color: var(--color-primary);
  margin-bottom: .5rem;
}

.skill-card__items { font-size: .9rem; color: var(--color-text); line-height: 1.7; }

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

.project-card {
  background: var(--color-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  box-shadow: var(--shadow-sm);
  transition: box-shadow var(--transition), transform var(--transition);
  display: flex;
  flex-direction: column;
}
.project-card:hover { box-shadow: var(--shadow-md); transform: translateY(-2px); }

.project-card__title { font-size: 1.05rem; font-weight: 700; margin-bottom: .35rem; }
.project-card__desc { font-size: .9rem; color: var(--color-text-muted); flex: 1; }

.project-card__links {
  display: flex;
  gap: .6rem;
  margin-top: .75rem;
  flex-wrap: wrap;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: .3rem;
  padding: .35rem .75rem;
  border-radius: var(--radius);
  font-size: .82rem;
  font-weight: 600;
  transition: background var(--transition), color var(--transition);
}
.btn--primary { background: var(--color-primary); color: #fff; }
.btn--primary:hover { background: var(--color-primary-dk); color: #fff; text-decoration: none; }
.btn--outline { border: 1px solid var(--color-border); color: var(--color-text); background: var(--color-card); }
.btn--outline:hover { border-color: var(--color-primary); color: var(--color-primary); text-decoration: none; }

/* --- Timeline ------------------------------------------------------------- */
.timeline { position: relative; padding-left: 1.5rem; }
.timeline::before {
  content: '';
  position: absolute;
  left: 5px;
  top: 0; bottom: 0;
  width: 2px;
  background: var(--color-border);
}
.timeline__item { position: relative; margin-bottom: 1.5rem; }
.timeline__item::before {
  content: '';
  position: absolute;
  left: -1.5rem;
  top: .55rem;
  width: 10px; height: 10px;
  border-radius: 50%;
  background: var(--color-primary);
  border: 2px solid var(--color-card);
}

/* --- Footer --------------------------------------------------------------- */
.footer {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 1.5rem;
  text-align: center;
  font-size: .82rem;
  color: var(--color-text-muted);
  border-top: 1px solid var(--color-border);
}

/* --- Responsive ----------------------------------------------------------- */
@media (max-width: 768px) {
  .hero { flex-direction: column; text-align: center; gap: 1.5rem; padding-top: 2rem; }
  .hero__links { justify-content: center; }
  .hero__photo { width: 120px; height: 120px; }
  .hero__info h1 { font-size: 1.6rem; }

  .nav__links { display: none; }
  .nav__links.open {
    display: flex;
    flex-direction: column;
    position: absolute;
    top: 100%;
    left: 0; right: 0;
    background: rgba(255,255,255,.97);
    padding: 1rem 1.5rem;
    gap: .75rem;
    border-bottom: 1px solid var(--color-border);
  }
  .nav__toggle { display: block; }

  .projects-grid { grid-template-columns: 1fr; }
  .skills-grid { grid-template-columns: 1fr; }
}