/* ===================================================================
   Xiaozhou (Simon) Wang — Personal Academic Website
   Style inspired by minimalist academic portfolios
   =================================================================== */

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

:root {
  --bg: #faf8f4;          /* warm off-white background */
  --bg-alt: #f3efe7;      /* slightly darker section bg */
  --ink: #1a1a1a;         /* primary text */
  --ink-soft: #4a4a4a;    /* secondary text */
  --ink-muted: #8a8580;   /* muted / meta text */
  --line: #d9d3c7;        /* hairline borders */
  --accent: #7a5af0;      /* subtle accent (links) */
  --accent-hover: #5b3fd6;
  --overlay: rgba(20, 20, 24, 0.55); /* hero overlay */
  --serif: "Cormorant Garamond", "Playfair Display", Georgia, "Times New Roman", serif;
  --sans: "Inter", "Helvetica Neue", "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --maxw: 1180px;
  --pad: clamp(1.25rem, 4vw, 4rem);
  --radius: 2px;
  --ease: cubic-bezier(0.22, 0.61, 0.36, 1);
}

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.7;
  font-weight: 400;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}

a {
  color: var(--ink);
  text-decoration: none;
  transition: color 0.25s var(--ease);
}

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

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

/* ---------- Site Header ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--bg);
  border-bottom: 1px solid var(--line);
}

.site-header__inner {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 1.1rem var(--pad);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.25rem;
}

.site-brand {
  font-family: var(--sans);
  font-size: 0.95rem;
  font-weight: 600;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink);
  white-space: nowrap;
  flex-shrink: 0;
}

.site-brand span {
  color: var(--ink-muted);
  font-weight: 400;
}

.primary-nav ul {
  display: flex;
  align-items: center;
  gap: clamp(1rem, 2vw, 1.6rem);
  list-style: none;
  margin: 0;
  padding: 0;
}

.primary-nav li {
  list-style: none;
}

.primary-nav a {
  font-size: 0.86rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ink-soft);
  font-weight: 500;
  padding: 0.25rem 0;
  position: relative;
}

.primary-nav a::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -2px;
  width: 0;
  height: 1px;
  background: var(--ink);
  transition: width 0.3s var(--ease);
}

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

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

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  flex-shrink: 0;
}

.lang-toggle {
  background: none;
  border: 1px solid var(--line);
  border-radius: 999px;
  cursor: pointer;
  font-family: var(--sans);
  font-size: 0.78rem;
  font-weight: 500;
  letter-spacing: 0.08em;
  color: var(--ink-soft);
  padding: 0.32rem 0.9rem;
  transition: all 0.25s var(--ease);
}

.lang-toggle:hover {
  color: var(--ink);
  border-color: var(--ink);
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  font-size: 1.25rem;
  color: var(--ink);
}

/* ---------- Layout ---------- */
.page {
  min-height: calc(100vh - 200px);
}

.section {
  padding: clamp(3.5rem, 8vw, 7rem) var(--pad);
}

.section--alt {
  background: var(--bg-alt);
}

.container {
  max-width: var(--maxw);
  margin: 0 auto;
}

.container--narrow {
  max-width: 760px;
}

/* ---------- Page Header (interior pages) ---------- */
.page-head {
  padding: clamp(3.5rem, 8vw, 6rem) var(--pad) 2rem;
  border-bottom: 1px solid var(--line);
}

.page-head__eyebrow {
  font-size: 0.78rem;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin-bottom: 0.75rem;
}

.page-head__title {
  font-family: var(--serif);
  font-weight: 500;
  font-size: clamp(2.2rem, 5vw, 3.4rem);
  line-height: 1.15;
  letter-spacing: -0.01em;
}

.page-head__sub {
  margin-top: 0.85rem;
  color: var(--ink-soft);
  font-size: 1.05rem;
  max-width: 620px;
}

/* ---------- Typography ---------- */
.lead {
  font-size: 1.15rem;
  color: var(--ink-soft);
  line-height: 1.75;
  max-width: 680px;
}

h2 {
  font-family: var(--serif);
  font-weight: 500;
  font-size: clamp(1.6rem, 3.5vw, 2.3rem);
  line-height: 1.2;
  margin-bottom: 1rem;
}

h3 {
  font-family: var(--sans);
  font-weight: 600;
  font-size: 1.2rem;
  margin-bottom: 0.5rem;
}

p {
  margin-bottom: 1.1rem;
}

.meta {
  font-size: 0.85rem;
  color: var(--ink-muted);
  letter-spacing: 0.04em;
}

/* ---------- Buttons ---------- */
.btn {
  display: inline-block;
  padding: 0.85rem 1.75rem;
  border: 1px solid var(--ink);
  background: transparent;
  color: var(--ink);
  font-size: 0.85rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  font-weight: 500;
  transition: all 0.3s var(--ease);
  cursor: pointer;
}

.btn:hover {
  background: var(--ink);
  color: var(--bg);
}

.btn--solid {
  background: var(--ink);
  color: var(--bg);
}

.btn--solid:hover {
  background: transparent;
  color: var(--ink);
}

.btn--ghost-light {
  border-color: rgba(255, 255, 255, 0.7);
  color: #fff;
}

.btn--ghost-light:hover {
  background: #fff;
  color: var(--ink);
}

/* ---------- HERO (Home) ---------- */
.hero {
  position: relative;
  min-height: 100vh;
  display: flex;
  align-items: flex-end;
  background-image: url("../img/home-hero.jpg");
  background-size: cover;
  background-position: center;
  background-repeat: no-repeat;
}

.hero::before {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(
    to bottom,
    rgba(20, 20, 24, 0.35) 0%,
    rgba(20, 20, 24, 0.15) 35%,
    rgba(20, 20, 24, 0.75) 100%
  );
}

.hero__inner {
  position: relative;
  z-index: 2;
  width: 100%;
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 0 var(--pad) clamp(3rem, 8vw, 6rem);
  color: #fff;
}

.hero__title {
  font-family: var(--serif);
  font-weight: 700;
  font-size: clamp(2.6rem, 7vw, 5.2rem);
  line-height: 1.08;
  letter-spacing: -0.015em;
  margin-bottom: 1.25rem;
  max-width: 14ch;
}

.hero__sub {
  font-size: clamp(1rem, 1.4vw, 1.2rem);
  line-height: 1.7;
  max-width: 480px;
  color: rgba(255, 255, 255, 0.88);
}

.hero__sub p {
  margin-bottom: 0.35rem;
}

.hero__cta {
  margin-top: 2.25rem;
}

/* ---------- Updates list (Home) ---------- */
.updates {
  border-top: 1px solid var(--line);
}

.updates__list {
  list-style: none;
}

.updates__item {
  display: grid;
  grid-template-columns: 140px 1fr;
  gap: 1.5rem;
  padding: 1.5rem 0;
  border-bottom: 1px solid var(--line);
  align-items: baseline;
}

.updates__date {
  font-size: 0.85rem;
  letter-spacing: 0.08em;
  color: var(--ink-muted);
  text-transform: uppercase;
  font-variant-numeric: tabular-nums;
}

.updates__text {
  color: var(--ink-soft);
  font-size: 1.02rem;
  line-height: 1.65;
}

/* ---------- Two-column (About) ---------- */
.text-col {
  max-width: 760px;
}

.split {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: clamp(2.5rem, 5vw, 5rem);
  align-items: start;
}

.split--lean {
  grid-template-columns: 1.4fr 1fr;
}

/* ---------- Timeline ---------- */
.timeline {
  list-style: none;
  position: relative;
  padding-left: 1.75rem;
}

.timeline::before {
  content: "";
  position: absolute;
  left: 5px;
  top: 6px;
  bottom: 6px;
  width: 1px;
  background: var(--line);
}

.timeline__item {
  position: relative;
  padding-bottom: 2rem;
}

.timeline__item:last-child {
  padding-bottom: 0;
}

.timeline__item::before {
  content: "";
  position: absolute;
  left: -1.75rem;
  top: 7px;
  width: 11px;
  height: 11px;
  border-radius: 50%;
  background: var(--bg);
  border: 1.5px solid var(--ink);
}

.timeline__date {
  font-size: 0.82rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin-bottom: 0.4rem;
}

.timeline__title {
  font-weight: 600;
  font-size: 1.05rem;
  margin-bottom: 0.2rem;
}

.timeline__detail {
  color: var(--ink-soft);
  font-size: 0.95rem;
  line-height: 1.6;
}

/* ---------- Skill tags ---------- */
.tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
  list-style: none;
}

.tags li {
  padding: 0.4rem 0.9rem;
  border: 1px solid var(--line);
  border-radius: 999px;
  font-size: 0.85rem;
  color: var(--ink-soft);
  background: var(--bg);
  transition: all 0.25s var(--ease);
}

.tags li:hover {
  border-color: var(--ink);
  color: var(--ink);
}

/* ---------- Research project cards ---------- */
.research-card {
  position: relative;
  border: 1px solid var(--line);
  background: var(--bg);
  margin-bottom: 2.5rem;
  overflow: hidden;
}

.research-card--feature {
  color: #fff;
  border: none;
  min-height: 460px;
  display: flex;
  align-items: flex-end;
  background-size: cover;
  background-position: center;
}

.research-card--feature--p1 {
  background-image: linear-gradient(var(--overlay), var(--overlay)),
    url("../img/research-bg.jpg");
}

.research-card--feature--p2 {
  background-image: linear-gradient(var(--overlay), var(--overlay)),
    url("../img/8afbff8823c8aa4b8ded0a57013875cf.jpg");
}

.research-card--feature--p3 {
  background-image: linear-gradient(var(--overlay), var(--overlay)),
    url("../img/5adde761f6ab2c0dbe41a46b434d1531.jpg");
}

.research-card:last-child {
  margin-bottom: 0;
}

.research-card--feature .research-card__body {
  padding: clamp(2rem, 4vw, 3rem);
  position: relative;
  z-index: 2;
}

.research-card--feature h3 {
  color: #fff;
  font-family: var(--serif);
  font-size: clamp(1.6rem, 3vw, 2.2rem);
  font-weight: 500;
}

.research-card--feature .research-card__field {
  color: rgba(255, 255, 255, 0.82);
}

.research-card--feature .research-card__index {
  color: rgba(255, 255, 255, 0.6);
}

.research-card--feature .research-card__field strong {
  color: rgba(255, 255, 255, 0.55);
}

.research-card--feature .research-card__status {
  color: rgba(255, 255, 255, 0.8);
}

.research-card__body {
  padding: clamp(1.5rem, 3vw, 2.25rem);
}

.research-card__index {
  font-size: 0.78rem;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin-bottom: 0.6rem;
}

.research-card h3 {
  font-family: var(--serif);
  font-size: clamp(1.4rem, 2.6vw, 1.9rem);
  font-weight: 500;
  margin-bottom: 1rem;
}

.research-card__field {
  margin-bottom: 0.9rem;
  color: var(--ink-soft);
  font-size: 0.96rem;
  line-height: 1.65;
}

.research-card__field strong {
  display: inline-block;
  min-width: 90px;
  color: var(--ink-muted);
  font-weight: 500;
  text-transform: uppercase;
  font-size: 0.78rem;
  letter-spacing: 0.08em;
}

.research-card__status {
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px solid var(--line);
  font-size: 0.92rem;
  color: var(--ink-soft);
}

.research-card--feature .research-card__status {
  border-top-color: rgba(255, 255, 255, 0.25);
}

/* ---------- Project cards ---------- */
.project-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.75rem;
}

.project-card {
  border: 1px solid var(--line);
  background: var(--bg);
  padding: clamp(1.5rem, 3vw, 2.25rem);
  display: flex;
  flex-direction: column;
}

.project-card__role {
  font-size: 0.78rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin-bottom: 0.85rem;
}

.project-card h3 {
  font-family: var(--serif);
  font-size: 1.45rem;
  font-weight: 500;
  line-height: 1.25;
  margin-bottom: 1rem;
}

.project-card p {
  color: var(--ink-soft);
  font-size: 0.95rem;
  line-height: 1.65;
}

/* ---------- Publications list ---------- */
.pub-section {
  margin-bottom: 3.5rem;
}

.pub-section__head {
  font-size: 0.82rem;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--ink-muted);
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--line);
  margin-bottom: 1.25rem;
}

.pub-item {
  padding: 1.25rem 0;
  border-bottom: 1px solid var(--line);
}

.pub-item__authors {
  color: var(--ink);
  font-weight: 500;
}

.pub-item__title {
  color: var(--ink-soft);
  font-style: italic;
}

.pub-item__venue {
  color: var(--ink-muted);
  font-size: 0.92rem;
  margin-top: 0.15rem;
}

/* ---------- CV ---------- */
.cv-block {
  margin-bottom: 3rem;
}

.cv-block__head {
  font-family: var(--serif);
  font-size: 1.5rem;
  font-weight: 500;
  margin-bottom: 1.25rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--line);
}

.cv-entry {
  display: grid;
  grid-template-columns: 180px 1fr;
  gap: 1.5rem;
  padding: 0.9rem 0;
  border-bottom: 1px solid var(--line);
}

.cv-entry__date {
  color: var(--ink-muted);
  font-size: 0.88rem;
  letter-spacing: 0.04em;
}

.cv-entry__title {
  font-weight: 600;
  margin-bottom: 0.15rem;
}

.cv-entry__detail {
  color: var(--ink-soft);
  font-size: 0.94rem;
}

/* ---------- Contact ---------- */
.contact-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: clamp(2rem, 5vw, 4rem);
  align-items: start;
}

.contact-list {
  list-style: none;
}

.contact-list li {
  padding: 1.1rem 0;
  border-bottom: 1px solid var(--line);
}

.contact-list__label {
  font-size: 0.78rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin-bottom: 0.25rem;
}

.contact-form {
  display: flex;
  flex-direction: column;
  gap: 1.1rem;
}

.field {
  display: flex;
  flex-direction: column;
}

.field label {
  font-size: 0.78rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin-bottom: 0.4rem;
}

.field input,
.field textarea {
  font-family: var(--sans);
  font-size: 1rem;
  color: var(--ink);
  background: transparent;
  border: none;
  border-bottom: 1px solid var(--line);
  padding: 0.55rem 0;
  transition: border-color 0.25s var(--ease);
}

.field input:focus,
.field textarea:focus {
  outline: none;
  border-bottom-color: var(--ink);
}

.field textarea {
  resize: vertical;
  min-height: 110px;
}

.contact-form .btn {
  align-self: flex-start;
  margin-top: 0.5rem;
}

/* ---------- Site Footer ---------- */
.site-footer {
  background: var(--bg);
  border-top: 1px solid var(--line);
  padding: 2.25rem var(--pad);
  text-align: center;
}

.site-footer__inner {
  max-width: var(--maxw);
  margin: 0 auto;
  font-size: 0.82rem;
  color: var(--ink-muted);
  letter-spacing: 0.04em;
  line-height: 1.6;
}

.site-footer a {
  color: var(--ink-muted);
}

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

/* ---------- Responsive ---------- */
@media (max-width: 940px) {
  .primary-nav {
    position: fixed;
    top: 0;
    right: 0;
    height: 100vh;
    width: min(78vw, 320px);
    background: var(--bg);
    border-left: 1px solid var(--line);
    padding: 4.5rem 2rem 2rem;
    transform: translateX(100%);
    transition: transform 0.35s var(--ease);
    z-index: 200;
  }

  .primary-nav.is-open {
    transform: translateX(0);
  }

  .primary-nav ul {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
  }

  .primary-nav li {
    border-bottom: 1px solid var(--line);
  }

  .primary-nav a {
    display: block;
    padding: 1.1rem 0;
    font-size: 0.95rem;
  }

  .nav-toggle {
    display: inline-block;
    z-index: 210;
  }

  .split,
  .split--lean,
  .contact-grid {
    grid-template-columns: 1fr;
  }

  .updates__item {
    grid-template-columns: 1fr;
    gap: 0.4rem;
  }

  .cv-entry {
    grid-template-columns: 1fr;
    gap: 0.3rem;
  }
}

@media (max-width: 520px) {
  .hero__sub {
    max-width: 100%;
  }
}

/* ---------- Motion safety ---------- */
@media (prefers-reduced-motion: reduce) {
  * {
    animation: none !important;
    transition: none !important;
    scroll-behavior: auto !important;
  }
}