/* ============================================================
   Kaiying Wu – Academic Personal Website
   Style Guide: Minimalist, Academic, Two-column Layout
   Reference: acad-homepage.github.io
   ============================================================ */

/* ===================== CSS CUSTOM PROPERTIES ===================== */
:root {
  /* Colors */
  --color-bg:          #ffffff;
  --color-bg-alt:      #f9fafb;
  --color-text:        #3b3f44;
  --color-text-light:  #6c757d;
  --color-heading:     #2c3e50;
  --color-link:        #224b8d;
  --color-link-hover:  #1a3a6e;
  --color-border:      #e8e8e8;
  --color-primary:     #224b8d;
  --color-badge:       #00369f;
  --color-highlight:   #224b8d;
  --color-sidebar-bg:  #fafbfc;

  /* Typography */
  --font-sans: 'Roboto', 'Trebuchet MS', Helvetica, Arial, sans-serif;
  --font-mono: 'Monaco', 'Consolas', 'Lucida Console', monospace;

  /* Sizing */
  --sidebar-width:     280px;
  --masthead-height:   52px;
  --max-width:         1200px;
  --border-radius:     6px;

  /* Transitions */
  --transition:        all 0.2s ease-in-out;
}

/* ===================== RESET & BASE ===================== */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--masthead-height) + 1.5rem);
  font-size: 15px;
}

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  background-color: var(--color-bg);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

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

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

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

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-sans);
  color: var(--color-heading);
  font-weight: 700;
  line-height: 1.3;
}

ul {
  list-style: none;
}

/* ===================== MASTHEAD / NAV ===================== */
.masthead {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  height: var(--masthead-height);
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--color-border);
  transition: var(--transition);
}

.masthead__inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.5rem;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.masthead__home {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--color-heading);
  white-space: nowrap;
}

.masthead__home:hover {
  color: var(--color-link);
}

.masthead__links {
  display: flex;
  gap: 1.8rem;
}

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

.masthead__links a::after {
  content: '';
  position: absolute;
  bottom: -2px;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--color-primary);
  transition: width 0.25s ease;
}

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

.masthead__links a:hover::after,
.masthead__links a.is-active::after {
  width: 100%;
}

.masthead__links a.is-active {
  color: var(--color-primary);
}

/* Hamburger */
.masthead__toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
}

.navicon {
  width: 22px;
  height: 2px;
  background: var(--color-text);
  position: relative;
  transition: var(--transition);
}

.navicon::before,
.navicon::after {
  content: '';
  position: absolute;
  width: 22px;
  height: 2px;
  background: var(--color-text);
  left: 0;
  transition: var(--transition);
}

.navicon::before { top: -6px; }
.navicon::after  { top: 6px; }

/* ===================== LAYOUT ===================== */
.layout {
  display: flex;
  max-width: var(--max-width);
  margin: 0 auto;
  margin-top: var(--masthead-height);
  min-height: calc(100vh - var(--masthead-height));
}

/* ===================== SIDEBAR ===================== */
.sidebar {
  position: sticky;
  top: var(--masthead-height);
  width: var(--sidebar-width);
  min-width: var(--sidebar-width);
  height: calc(100vh - var(--masthead-height));
  overflow-y: auto;
  padding: 2rem 1.5rem;
  border-right: 1px solid var(--color-border);
  background: var(--color-sidebar-bg);
}

.sidebar__inner {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
}

.sidebar__avatar {
  width: 160px;
  height: 160px;
  margin-bottom: 1.2rem;
}

.sidebar__avatar img {
  width: 100%;
  height: 100%;
  border-radius: 50%;
  object-fit: cover;
  border: 3px solid var(--color-border);
  transition: var(--transition);
}

.sidebar__avatar img:hover {
  border-color: var(--color-primary);
  transform: scale(1.02);
}

.sidebar__name {
  font-size: 1.35rem;
  margin-bottom: 0.25rem;
  color: var(--color-heading);
}

.sidebar__title {
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--color-text);
  margin-bottom: 0.15rem;
}

.sidebar__affiliation {
  font-size: 0.82rem;
  color: var(--color-text-light);
  margin-bottom: 0.1rem;
}

.sidebar__sub {
  font-size: 0.75rem;
  color: var(--color-text-light);
  margin-bottom: 1rem;
}

.sidebar__bio {
  font-size: 0.82rem;
  line-height: 1.55;
  color: var(--color-text-light);
  margin-bottom: 1.2rem;
  text-align: left;
  padding: 0 0.25rem;
}

.sidebar__links {
  width: 100%;
  margin-bottom: 1rem;
}

.sidebar__links li {
  margin-bottom: 0.45rem;
}

.sidebar__links a {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-size: 0.85rem;
  color: var(--color-text);
  padding: 0.35rem 0.5rem;
  border-radius: var(--border-radius);
  transition: var(--transition);
}

.sidebar__links a:hover {
  color: var(--color-link);
  background: rgba(34, 75, 141, 0.06);
}

.sidebar__links i {
  width: 1.2rem;
  text-align: center;
  font-size: 1rem;
  color: var(--color-text-light);
  flex-shrink: 0;
}

.sidebar__links a:hover i {
  color: var(--color-link);
}

.sidebar__location {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.82rem;
  color: var(--color-text-light);
  margin-top: 0.5rem;
}

/* ===================== MAIN CONTENT ===================== */
.content {
  flex: 1;
  padding: 2rem 2.5rem;
  max-width: calc(var(--max-width) - var(--sidebar-width));
}

/* ===================== SECTIONS ===================== */
.section {
  margin-bottom: 2.5rem;
  padding-bottom: 2rem;
  border-bottom: 1px solid var(--color-border);
}

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

.section__title {
  font-size: 1.45rem;
  margin-bottom: 1.2rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--color-primary);
  display: inline-block;
  color: var(--color-heading);
}

.section__icon {
  margin-right: 0.35rem;
}

.section__body p {
  margin-bottom: 0.7rem;
  font-size: 0.95rem;
}

.section__body strong {
  color: var(--color-heading);
}

/* ===================== NEWS ===================== */
.news-list {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
}

.news-item {
  display: flex;
  gap: 1.2rem;
  padding: 0.6rem 0;
  border-bottom: 1px solid rgba(0,0,0,0.04);
  align-items: flex-start;
}

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

.news-date {
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--color-primary);
  white-space: nowrap;
  min-width: 5.5rem;
  font-variant-numeric: tabular-nums;
}

.news-text {
  font-size: 0.9rem;
  color: var(--color-text);
  line-height: 1.5;
}

/* ===================== PUBLICATIONS ===================== */
.pub-card {
  display: flex;
  gap: 1.5rem;
  padding: 1.5rem 0;
  border-bottom: 1px solid var(--color-border);
  align-items: flex-start;
}

.pub-card:last-child {
  border-bottom: none;
}

.pub-card__image {
  position: relative;
  min-width: 200px;
  max-width: 240px;
  flex-shrink: 0;
}

.pub-card__image img {
  width: 100%;
  border-radius: var(--border-radius);
  box-shadow: 2px 2px 8px rgba(0, 0, 0, 0.08);
  aspect-ratio: 5 / 3;
  object-fit: cover;
  background: var(--color-bg-alt);
}

.pub-badge {
  position: absolute;
  top: 0.5rem;
  left: -0.25rem;
  padding: 0.15rem 0.6rem;
  background: var(--color-badge);
  color: #fff;
  font-size: 0.72rem;
  font-weight: 600;
  border-radius: 2px;
  letter-spacing: 0.02em;
}

.pub-card__content {
  flex: 1;
}

.pub-title {
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 0.35rem;
  color: var(--color-heading);
  line-height: 1.4;
}

.pub-authors {
  font-size: 0.88rem;
  color: var(--color-text-light);
  margin-bottom: 0.2rem;
}

.pub-highlight {
  color: var(--color-primary);
  font-weight: 600;
}

.pub-venue {
  font-size: 0.85rem;
  color: var(--color-text-light);
  margin-bottom: 0.5rem;
}

.pub-desc {
  font-size: 0.85rem;
  color: var(--color-text);
  line-height: 1.55;
  margin-bottom: 0.7rem;
}

.pub-links {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.pub-link {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.25rem 0.7rem;
  font-size: 0.78rem;
  font-weight: 500;
  color: var(--color-primary);
  border: 1px solid var(--color-primary);
  border-radius: var(--border-radius);
  transition: var(--transition);
}

.pub-link:hover {
  background: var(--color-primary);
  color: #fff;
}

.pub-link i {
  font-size: 0.75rem;
}

/* ===================== PROJECTS ===================== */
.project-card {
  display: flex;
  gap: 1.5rem;
  padding: 1.5rem 0;
  border-bottom: 1px solid var(--color-border);
  align-items: flex-start;
}

.project-card:last-child {
  border-bottom: none;
}

.project-card__image {
  min-width: 180px;
  max-width: 220px;
  flex-shrink: 0;
}

.project-card__image img {
  width: 100%;
  border-radius: var(--border-radius);
  box-shadow: 2px 2px 8px rgba(0, 0, 0, 0.08);
  aspect-ratio: 5 / 3;
  object-fit: cover;
  background: var(--color-bg-alt);
}

.project-card__content {
  flex: 1;
}

.project-title {
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 0.4rem;
  color: var(--color-heading);
}

.project-desc {
  font-size: 0.88rem;
  color: var(--color-text);
  line-height: 1.55;
  margin-bottom: 0.7rem;
}

/* ===================== EDUCATION ===================== */
.edu-list {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.edu-item {
  display: flex;
  gap: 1.5rem;
  align-items: flex-start;
}

.edu-date {
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--color-primary);
  white-space: nowrap;
  min-width: 10rem;
  padding-top: 0.15rem;
  font-variant-numeric: tabular-nums;
}

.edu-detail h3 {
  font-size: 1rem;
  margin-bottom: 0.2rem;
}

.edu-school {
  font-size: 0.88rem;
  color: var(--color-text-light);
  margin-bottom: 0.2rem;
}

.edu-info {
  font-size: 0.85rem;
  color: var(--color-text);
  line-height: 1.5;
  margin-top: 0.15rem;
}

.edu-info i {
  color: #daa520;
  margin-right: 0.2rem;
}

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

.skill-group {
  padding: 1rem;
  background: var(--color-bg-alt);
  border-radius: var(--border-radius);
  border: 1px solid var(--color-border);
}

.skill-group h4 {
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--color-primary);
  margin-bottom: 0.35rem;
}

.skill-group p {
  font-size: 0.82rem;
  color: var(--color-text);
  line-height: 1.5;
}

/* ===================== FOOTER ===================== */
.footer {
  border-top: 1px solid var(--color-border);
  padding: 1.5rem 0;
  text-align: center;
  background: var(--color-bg-alt);
}

.footer__inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.5rem;
}

.footer p {
  font-size: 0.8rem;
  color: var(--color-text-light);
}

/* ===================== RESPONSIVE: TABLET ===================== */
@media (max-width: 925px) {
  .pub-card__image {
    min-width: 160px;
    max-width: 200px;
  }

  .project-card__image {
    min-width: 150px;
    max-width: 180px;
  }

  .content {
    padding: 1.5rem 1.5rem;
  }
}

/* ===================== RESPONSIVE: MOBILE ===================== */
@media (max-width: 768px) {
  html {
    font-size: 14px;
  }

  /* Nav */
  .masthead__toggle {
    display: block;
  }

  .masthead__links {
    display: none;
    position: absolute;
    top: var(--masthead-height);
    left: 0;
    right: 0;
    flex-direction: column;
    background: rgba(255, 255, 255, 0.98);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--color-border);
    padding: 0.75rem 1.5rem;
    gap: 0;
    box-shadow: 0 4px 12px rgba(0,0,0,0.06);
  }

  .masthead__links.is-open {
    display: flex;
  }

  .masthead__links li {
    padding: 0.6rem 0;
    border-bottom: 1px solid rgba(0,0,0,0.04);
  }

  .masthead__links li:last-child {
    border-bottom: none;
  }

  .masthead__links a {
    font-size: 0.95rem;
  }

  .masthead__links a::after {
    display: none;
  }

  /* Layout */
  .layout {
    flex-direction: column;
  }

  /* Sidebar → Top Header */
  .sidebar {
    position: relative;
    top: 0;
    width: 100%;
    min-width: 100%;
    height: auto;
    border-right: none;
    border-bottom: 1px solid var(--color-border);
    padding: 1.5rem;
  }

  .sidebar__inner {
    flex-direction: row;
    flex-wrap: wrap;
    text-align: left;
    gap: 1rem;
  }

  .sidebar__avatar {
    width: 80px;
    height: 80px;
    margin-bottom: 0;
  }

  .sidebar__info {
    flex: 1;
    min-width: 150px;
  }

  .sidebar__name {
    font-size: 1.2rem;
  }

  .sidebar__bio {
    width: 100%;
    margin-bottom: 0.8rem;
  }

  .sidebar__links {
    display: flex;
    flex-wrap: wrap;
    gap: 0.25rem;
  }

  .sidebar__links li {
    margin-bottom: 0;
  }

  .sidebar__links a span {
    display: none;
  }

  .sidebar__links a {
    padding: 0.35rem;
    font-size: 1.1rem;
  }

  .sidebar__links i {
    font-size: 1.15rem;
    width: auto;
  }

  /* Content */
  .content {
    padding: 1.25rem 1rem;
    max-width: 100%;
  }

  /* Publication cards */
  .pub-card {
    flex-direction: column;
    gap: 0.8rem;
  }

  .pub-card__image {
    min-width: 100%;
    max-width: 100%;
  }

  .pub-card__image img {
    max-width: 320px;
  }

  /* Project cards */
  .project-card {
    flex-direction: column;
    gap: 0.8rem;
  }

  .project-card__image {
    min-width: 100%;
    max-width: 100%;
  }

  .project-card__image img {
    max-width: 280px;
  }

  /* Education */
  .edu-item {
    flex-direction: column;
    gap: 0.3rem;
  }

  .edu-date {
    min-width: auto;
  }

  /* Section title */
  .section__title {
    font-size: 1.25rem;
  }
}

/* ===================== RESPONSIVE: SMALL MOBILE ===================== */
@media (max-width: 480px) {
  .content {
    padding: 1rem 0.75rem;
  }

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

  .sidebar {
    padding: 1rem;
  }
}

/* ===================== PRINT ===================== */
@media print {
  .masthead,
  .masthead__toggle,
  .footer {
    display: none;
  }

  .layout {
    margin-top: 0;
  }

  .sidebar {
    position: relative;
    height: auto;
    border-right: none;
    page-break-after: avoid;
  }

  .content {
    padding: 1rem;
  }

  .section {
    page-break-inside: avoid;
  }
}

/* ===================== ANIMATIONS ===================== */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(16px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.section {
  animation: fadeInUp 0.4s ease both;
}

.section:nth-child(1) { animation-delay: 0.1s; }
.section:nth-child(2) { animation-delay: 0.2s; }
.section:nth-child(3) { animation-delay: 0.3s; }
.section:nth-child(4) { animation-delay: 0.35s; }
.section:nth-child(5) { animation-delay: 0.4s; }
.section:nth-child(6) { animation-delay: 0.45s; }

/* ===================== SCROLLBAR ===================== */
.sidebar::-webkit-scrollbar {
  width: 4px;
}

.sidebar::-webkit-scrollbar-track {
  background: transparent;
}

.sidebar::-webkit-scrollbar-thumb {
  background: var(--color-border);
  border-radius: 2px;
}

.sidebar::-webkit-scrollbar-thumb:hover {
  background: var(--color-text-light);
}

/* ===================== PLACEHOLDER IMAGES ===================== */
.pub-card__image img[src=""],
.pub-card__image img:not([src]),
.project-card__image img[src=""],
.project-card__image img:not([src]) {
  background: linear-gradient(135deg, #e8eef5 0%, #dde4ed 100%);
  min-height: 120px;
}