/* Leonid Kogan - Personal Website
   Responsive, modern layout. No frames. */

:root {
  --color-primary: #1e3a5f;
  --color-primary-light: #2c5282;
  --color-accent: #c41e3a;
  --color-bg: #fafafa;
  --color-bg-section: #fff;
  --color-text: #1a1a1a;
  --color-text-muted: #555;
  --color-border: #e2e8f0;
  --font-sans: "Segoe UI", system-ui, -apple-system, sans-serif;
  --font-serif: Georgia, "Times New Roman", serif;
  --nav-height: 3.5rem;
  --max-width: 900px;
  --spacing: 1.5rem;
  --radius: 6px;
}

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

.skip-link {
  position: absolute;
  top: -3rem;
  left: 0.5rem;
  z-index: 101;
  padding: 0.5rem 1rem;
  background: var(--color-primary);
  color: #fff;
  text-decoration: none;
  font-size: 0.9rem;
  border-radius: var(--radius);
  transition: top 0.2s;
}

.skip-link:focus {
  top: 0.5rem;
}

html {
  scroll-behavior: smooth;
}

/* Prevent sticky header from covering section titles when navigating by anchor */
main [id] {
  scroll-margin-top: calc(var(--nav-height) + 0.5rem);
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.6;
  color: var(--color-text);
  background: var(--color-bg);
}

/* ----- Header & Nav ----- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--color-bg-section);
  border-bottom: 1px solid var(--color-border);
  box-shadow: 0 1px 3px rgba(0,0,0,0.06);
}

.site-header .inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing);
  height: var(--nav-height);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.site-title {
  font-size: 1.1rem;
  font-weight: 600;
  margin: 0;
}

.site-title a {
  color: var(--color-primary);
  text-decoration: none;
}

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

.nav-list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.25rem 1rem;
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-list a {
  color: var(--color-text);
  text-decoration: none;
  font-size: 0.95rem;
  padding: 0.35em 0.5em;
  border-radius: var(--radius);
}

.nav-list a:hover,
.nav-list a:focus {
  background: var(--color-bg);
  color: var(--color-primary);
}

.nav-list a.cv-link {
  font-weight: 600;
  color: var(--color-accent);
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  padding: 0.5rem;
  cursor: pointer;
  font-size: 1.25rem;
  color: var(--color-primary);
  line-height: 1;
}

/* ----- Main ----- */
main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing) 3rem;
}

section {
  padding: 2.5rem 0;
  border-bottom: 1px solid var(--color-border);
}

section:last-of-type {
  border-bottom: none;
}

.section-title {
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--color-primary);
  margin: 0 0 1rem;
  padding-bottom: 0.5rem;
}

/* ----- Hero (Home) ----- */
#home {
  padding: 2rem 0 2.5rem;
}

.hero {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 2rem;
  align-items: start;
}

.hero-photo {
  width: 180px;
  height: 180px;
  object-fit: cover;
  border-radius: var(--radius);
  border: 2px solid var(--color-border);
}

.hero-text h1 {
  font-size: 1.75rem;
  font-weight: 700;
  margin: 0 0 0.25rem;
  color: var(--color-primary);
}

.hero-text .title {
  font-size: 1rem;
  color: var(--color-text-muted);
  margin: 0 0 0.5rem;
  line-height: 1.5;
  white-space: normal;
}

.hero-cta {
  margin-top: 1rem;
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.btn {
  display: inline-block;
  padding: 0.5rem 1rem;
  border-radius: var(--radius);
  font-size: 0.95rem;
  font-weight: 500;
  text-decoration: none;
  transition: background 0.2s, color 0.2s;
}

.btn-primary {
  background: var(--color-accent);
  color: #fff;
}

.btn-primary:hover {
  background: #a01830;
  color: #fff;
}

.btn-secondary {
  background: var(--color-bg);
  color: var(--color-primary);
  border: 1px solid var(--color-border);
}

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

/* Highlights on homepage */
.highlights {
  margin-top: 2rem;
}

.highlights h3 {
  font-size: 1.15rem;
  margin: 0 0 0.75rem;
  color: var(--color-primary);
}

.highlight-list {
  list-style: none;
  padding: 0;
  margin: 0 0 1.5rem;
}

.highlight-list li {
  margin-bottom: 0.75rem;
  padding-left: 0;
}

.highlights .abstract {
  margin-top: 0.25em;
  font-size: 0.95em;
}

.highlight-list a {
  color: var(--color-primary);
  text-decoration: none;
  font-weight: 500;
}

.highlight-list a:hover {
  text-decoration: underline;
}

.highlight-list .meta {
  font-size: 0.9rem;
  color: var(--color-text-muted);
  margin-top: 0.15rem;
}

/* ----- Bio ----- */
#bio .bio-long {
  width: 100%;
  min-width: 0;
  white-space: normal;
}

#bio .bio-long p {
  margin: 0 0 1rem;
  overflow-wrap: break-word;
  word-wrap: break-word;
  white-space: normal;
}

#bio {
  min-width: 0;
}

#bio .awards {
  margin-top: 1rem;
  padding-left: 1.25rem;
}

#bio .awards li {
  margin-bottom: 0.35rem;
}

/* ----- Research & Publications ----- */
.paper-list,
.pub-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.paper-item,
.pub-item {
  margin-bottom: 1.25rem;
  padding-bottom: 1.25rem;
  border-bottom: 1px solid var(--color-border);
}

.paper-item:last-child,
.pub-item:last-child {
  border-bottom: none;
  margin-bottom: 0;
  padding-bottom: 0;
}

.paper-item h4,
.pub-item .title {
  font-size: 1rem;
  font-weight: 600;
  margin: 0 0 0.35rem;
  line-height: 1.4;
}

.paper-item h4 a,
.pub-item a {
  color: var(--color-primary);
  text-decoration: none;
}

.paper-item h4 a:hover,
.pub-item a:hover {
  text-decoration: underline;
}

.paper-item .abstract,
.pub-item .abstract,
.pub-item .journal {
  font-size: 0.9rem;
  color: var(--color-text-muted);
  margin-top: 0.25rem;
}

/* Full abstract, collapsed under the one-line summary (working papers) */
.full-abstract {
  margin-top: 0.3rem;
  font-size: 0.9rem;
}

.full-abstract summary {
  cursor: pointer;
  color: var(--color-accent);
  width: fit-content;
}

.full-abstract summary:hover {
  text-decoration: underline;
}

.full-abstract p {
  margin: 0.35rem 0 0;
  color: var(--color-text);
  line-height: 1.55;
  text-align: justify;
  hyphens: auto;
}

.paper-links,
.pub-links {
  margin-top: 0.35rem;
  font-size: 0.9rem;
}

.paper-links a,
.pub-links a {
  color: var(--color-accent);
  text-decoration: none;
  margin-right: 0.75rem;
}

.paper-links a:hover,
.pub-links a:hover {
  text-decoration: underline;
}

.subsection-title {
  font-size: 1.1rem;
  font-weight: 600;
  margin: 1.5rem 0 0.75rem;
  color: var(--color-text);
}

/* ----- Teaching ----- */
.course-list {
  list-style: none;
  padding: 0;
  margin: 0 0 1.5rem;
}

.course-list li {
  margin-bottom: 1rem;
  padding: 1rem;
  background: var(--color-bg);
  border-radius: var(--radius);
  border-left: 3px solid var(--color-primary);
}

.course-list h4 {
  font-size: 1rem;
  margin: 0 0 0.35rem;
}

.course-list h4 a {
  color: var(--color-primary);
  text-decoration: none;
}

.course-list h4 a:hover {
  text-decoration: underline;
}

.course-list p {
  margin: 0;
  font-size: 0.95rem;
  color: var(--color-text-muted);
}

.teaching-blurb,
.mentoring-blurb {
  margin-bottom: 1.25rem;
  max-width: 65ch;
}

.students-list {
  padding-left: 1.25rem;
  margin: 0.5rem 0 0;
}

.students-list li {
  margin-bottom: 0.25rem;
}

/* ----- Contact ----- */
#contact .contact-grid {
  display: grid;
  gap: 1rem;
  max-width: 500px;
}

#contact .contact-item {
  display: flex;
  flex-wrap: wrap;
  gap: 0.25rem 0.5rem;
}

#contact .contact-item strong {
  min-width: 4rem;
}

#contact .profile-links {
  margin-top: 1rem;
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
}

#contact .profile-links a {
  color: var(--color-primary);
  text-decoration: none;
  font-weight: 500;
}

#contact .profile-links a:hover {
  text-decoration: underline;
}

/* ----- Footer ----- */
.site-footer {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 1rem var(--spacing) 1.5rem;
  font-size: 0.85rem;
  color: var(--color-text-muted);
  border-top: 1px solid var(--color-border);
}

/* ----- Responsive ----- */
@media (max-width: 768px) {
  .nav-toggle {
    display: block;
  }

  .nav-list {
    display: none;
    position: absolute;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: var(--color-bg-section);
    border-bottom: 1px solid var(--color-border);
    padding: 1rem;
    flex-direction: column;
    gap: 0;
  }

  .nav-list.is-open {
    display: flex;
  }

  .nav-list a {
    padding: 0.6rem 0;
    border-bottom: 1px solid var(--color-border);
  }

  .nav-list li:last-child a {
    border-bottom: none;
  }

  .hero {
    grid-template-columns: 1fr;
    text-align: center;
  }

  .hero-photo {
    margin: 0 auto;
  }

  .hero-cta {
    justify-content: center;
  }

  .section-title {
    font-size: 1.3rem;
  }
}

@media (max-width: 480px) {
  :root {
    --spacing: 1rem;
  }

  .hero-photo {
    width: 140px;
    height: 140px;
  }

  .hero-text h1 {
    font-size: 1.5rem;
  }
}

/* ----- Print ----- */
@media print {
  .site-header,
  .nav-toggle,
  .hero-cta,
  .btn,
  .highlights {
    display: none !important;
  }

  body {
    background: #fff;
  }

  section {
    padding: 1rem 0;
    border-bottom: 1px solid #ccc;
  }

  a[href^="http"]::after {
    content: " (" attr(href) ")";
    font-size: 0.85em;
    color: #666;
  }
}