/* Hanwen Zhang — personal site */

:root {
  --bg:        #ffffff;
  --text:      #1c1c1e;
  --muted:     #63636b;
  --rule:      #e2e2de;
  --accent:    #2a5d8f;

  --container:  62rem;   /* outer page width  */
  --sidebar:    13.5rem; /* left column       */
  --gap:        3.25rem; /* between columns   */
  --measure:    42rem;   /* reading width     */
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg:     #16171a;
    --text:   #e8e8e6;
    --muted:  #a0a0a8;
    --rule:   #2e3036;
    --accent: #7fb0dd;
  }
}

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

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

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: Charter, "Bitstream Charter", "Iowan Old Style", Georgia, "Times New Roman", serif;
  font-size: 17px;
  line-height: 1.62;
  text-rendering: optimizeLegibility;
}

.wrap {
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 1.75rem;
}

.nowrap { white-space: nowrap; }

/* ---------- header / nav ---------- */

.site-header {
  border-bottom: 1px solid var(--rule);
  padding: 2.5rem 0 1.25rem;
  margin-bottom: 2.75rem;
}

.site-name {
  font-size: 1.65rem;
  font-weight: 600;
  letter-spacing: -0.01em;
  margin: 0 0 0.15rem;
}

.site-name a { color: inherit; text-decoration: none; }
.site-name a:hover { color: var(--accent); }

.site-tagline {
  margin: 0 0 1.25rem;
  color: var(--muted);
  font-size: 0.95rem;
}

nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 1.5rem;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-size: 0.9rem;
  letter-spacing: 0.02em;
}

nav a {
  color: var(--muted);
  text-decoration: none;
  padding-bottom: 2px;
  border-bottom: 1.5px solid transparent;
}

nav a:hover { color: var(--text); }

nav a[aria-current="page"] {
  color: var(--text);
  border-bottom-color: var(--accent);
}

/* ---------- two-column layout ---------- */

.layout {
  display: grid;
  grid-template-columns: var(--sidebar) 1fr;
  gap: var(--gap);
  align-items: start;
}

.sidebar { position: sticky; top: 2rem; }

.content {
  max-width: var(--measure);
  min-width: 0;            /* let long words wrap instead of widening the grid */
}

.content > :first-child { margin-top: 0; }

/* stack on narrow screens */
@media (max-width: 54rem) {
  .layout { grid-template-columns: 1fr; gap: 2.25rem; }
  .sidebar { position: static; }
}

/* ---------- sidebar: portrait + contact ---------- */

.portrait {
  display: block;
  width: 100%;
  max-width: 11rem;
  aspect-ratio: 1;
  object-fit: cover;
  border-radius: 50%;
  border: 1px solid var(--rule);
  margin: 0 0 1.5rem;
}

.contact { list-style: none; margin: 0; padding: 0; }

.contact li {
  display: flex;
  align-items: flex-start;
  gap: 0.55rem;
  margin-bottom: 0.7rem;
}

.contact .icon {
  width: 15px;
  height: 15px;
  flex: 0 0 auto;
  margin-top: 0.28rem;   /* optical alignment with the first text line */
  color: var(--muted);
}

.contact .value {
  min-width: 0;          /* allow a long address to wrap, not overflow */
  font-size: 0.88rem;
  line-height: 1.45;
  word-break: break-word;
}

/* ---------- typography ---------- */

h1 {
  font-size: 1.5rem;
  font-weight: 600;
  letter-spacing: -0.01em;
  margin: 0 0 1.5rem;
}

h2 {
  font-size: 1.05rem;
  font-weight: 600;
  margin: 2.75rem 0 1rem;
  padding-bottom: 0.4rem;
  border-bottom: 1px solid var(--rule);
}

h3 {
  font-size: 1.02rem;
  font-weight: 600;
  margin: 0 0 0.35rem;
  line-height: 1.4;
}

p { margin: 0 0 1.1rem; }

a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 2px; }

/* opening paragraph on the about page */
.lede {
  font-size: 1.12rem;
  line-height: 1.55;
  margin-bottom: 1.4rem;
}

/* ---------- papers ---------- */

.paper { margin: 0 0 1.6rem; }

/* rule only between consecutive papers, never trailing */
.paper + .paper {
  border-top: 1px solid var(--rule);
  padding-top: 1.6rem;
}

.paper-meta {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-size: 0.85rem;
  color: var(--muted);
  margin: 0 0 0.75rem;
}

.abstract { font-size: 0.96rem; margin-bottom: 0; }

/* collapsible abstract: folded by default, opened with the pill button */
.abstract-toggle summary {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  list-style: none;
  cursor: pointer;
  user-select: none;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-size: 0.8rem;
  font-weight: 500;
  letter-spacing: 0.02em;
  color: var(--accent);
  padding: 0.22rem 0.75rem 0.22rem 0.65rem;
  border: 1px solid var(--rule);
  border-radius: 999px;
  transition: border-color 0.15s ease;
}

.abstract-toggle summary::-webkit-details-marker { display: none; }

/* chevron: points right when folded, down when open */
.abstract-toggle summary::before {
  content: "";
  width: 0.36rem;
  height: 0.36rem;
  border-right: 1.5px solid currentColor;
  border-bottom: 1.5px solid currentColor;
  transform: rotate(-45deg);
  transition: transform 0.15s ease;
}

.abstract-toggle[open] summary::before { transform: translateY(-0.1rem) rotate(45deg); }

.abstract-toggle summary:hover { border-color: var(--accent); }

.abstract-toggle summary:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

.abstract-toggle .abstract { margin-top: 0.85rem; }

.availability {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-size: 0.85rem;
  color: var(--muted);
  margin: 0 0 1.75rem;
}

/* ---------- teaching entries ---------- */

.entry {
  display: grid;
  grid-template-columns: 8.5rem 1fr;
  gap: 0.25rem 1.25rem;
  margin: 0 0 1.75rem;
}

.entry-when {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-size: 0.85rem;
  color: var(--muted);
  padding-top: 0.2rem;
}

.entry-what > :last-child { margin-bottom: 0; }

.entry-where { color: var(--muted); font-size: 0.94rem; margin: 0 0 0.4rem; }

.courses { margin: 0; padding-left: 1.1rem; font-size: 0.94rem; }
.courses li { margin-bottom: 0.25rem; }

@media (max-width: 34rem) {
  .entry { grid-template-columns: 1fr; gap: 0.15rem; }
}

/* ---------- footer ---------- */

.site-footer {
  margin-top: 4rem;
  padding: 1.5rem 0 3rem;
  border-top: 1px solid var(--rule);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-size: 0.82rem;
  color: var(--muted);
}