/* The Helping Hands Lab
   White canvas, neutral greys, few rules, wide type steps.
   Everything tunable lives in :root. */

:root {
  --width: 980px;
  --gutter: 22px;

  /* Neutral greys, not warm. High-contrast body text on white. */
  --ink:    #1d1d1f;   /* headings and body */
  --muted:  #6e6e73;   /* metadata, secondary links */
  --faint:  #86868b;   /* captions */
  --accent: #b01e28;   /* Northeastern red, deepened so it reads as considered */
  --line:   #d2d2d7;   /* hairline, used sparingly */
  --bg:     #ffffff;
  --bg-soft:#f5f5f7;   /* image placeholder / letterbox */

  /* Six well-separated steps rather than a dozen near-identical ones. */
  --t-hero:    clamp(46px, 7vw, 72px);
  --t-title:   clamp(32px, 4.6vw, 44px);
  --t-section: 26px;
  --t-item:    19px;
  --t-body:    17px;
  --t-small:   15px;
  --t-meta:    13.5px;

  --header-h: 60px;
  --radius: 14px;
  --radius-sm: 10px;

  --font: -apple-system, BlinkMacSystemFont, "SF Pro Text", "SF Pro Display",
          "Segoe UI", Roboto, "Helvetica Neue", Helvetica, Arial, sans-serif;
}

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

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

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font);
  font-size: var(--t-body);
  line-height: 1.58;
  /* SF is already optically spaced; positive tracking makes it look loose */
  letter-spacing: 0;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* padding-inline, never the `padding` shorthand: the shorthand would also zero
   out vertical padding set by whatever element carries .wrap. */
.wrap {
  max-width: var(--width);
  margin: 0 auto;
  padding-inline: var(--gutter);
}

a { color: var(--ink); text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: 3px; }

h1, h2, h3 { color: var(--ink); margin: 0; }

/* height:auto is load-bearing: the width/height HTML attributes are
   presentational hints that would otherwise pin the height and defeat every
   `aspect-ratio` below. */
img { max-width: 100%; display: block; height: auto; }

.skip-link {
  position: absolute; left: -9999px;
  background: var(--ink); color: #fff; padding: 10px 16px;
  border-radius: var(--radius-sm); z-index: 100;
}
.skip-link:focus { left: 10px; top: 10px; }

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

/* sticky, not fixed: the header stays in normal flow, so it reserves its own
   space and can never sit on top of the content. */
.site-header {
  position: sticky; top: 0; z-index: 50;
  height: var(--header-h);
  background: rgba(255, 255, 255, 0.72);
  backdrop-filter: saturate(180%) blur(20px);
  -webkit-backdrop-filter: saturate(180%) blur(20px);
}

.header-inner {
  height: 100%;
  display: flex; align-items: center; justify-content: space-between; gap: 18px;
}

.brand {
  font-size: var(--t-small); font-weight: 600;
  letter-spacing: -0.01em; color: var(--ink); white-space: nowrap;
}
.brand:hover { text-decoration: none; }

/* weight stays constant across states; only colour shifts */
.site-header nav { display: flex; gap: 30px; }
.site-header nav a {
  font-size: var(--t-small); font-weight: 400;
  color: var(--muted); transition: color .2s ease;
}
.site-header nav a:hover { color: var(--ink); text-decoration: none; }
.site-header nav a[aria-current="page"] { color: var(--ink); }

main { padding-top: 76px; padding-bottom: 120px; }

/* ------------------------------------------------------------------ home */

.hero { display: flex; gap: 48px; align-items: flex-start; }
.hero-copy { flex: 1 1 auto; min-width: 0; max-width: 34rem; }
.hero-logo { flex: 0 0 340px; min-width: 0; margin-top: 10px; }
.hero-logo img { width: 100%; }

.hero h1 {
  font-size: var(--t-hero);
  font-weight: 700;
  line-height: 1.02;
  letter-spacing: -0.032em;
  margin-bottom: 28px;
}

.hero .lede { font-size: 21px; line-height: 1.42; letter-spacing: -0.01em; margin: 0 0 18px; }
.hero .lede b { color: var(--accent); font-weight: 600; }
.hero p { margin: 0 0 18px; }
.hero-body { color: var(--muted); }

.hero-figure { margin: 72px 0 0; }
.hero-figure img { width: 100%; border-radius: var(--radius); }
.hero-figure figcaption { font-size: var(--t-meta); color: var(--faint); margin-top: 12px; }

/* a row of plain text links with a trailing arrow */
.text-links { display: flex; flex-wrap: wrap; gap: 28px; margin-top: 34px; }
.text-links a { font-weight: 600; font-size: var(--t-body); letter-spacing: -0.01em; }
.text-links a::after { content: " \2197"; color: var(--faint); font-weight: 400; }

.hero-external { margin-top: 30px; font-size: var(--t-small); color: var(--faint); }
.hero-external a { font-weight: 400; color: var(--muted); }
.hero-external a:hover { color: var(--ink); }

/* --------------------------------------------------------------- sections */

/* whitespace does the separating; no rules under headings */
.section { margin-top: 88px; }
.section:first-child { margin-top: 0; }

.section-title {
  font-size: var(--t-section); font-weight: 600;
  letter-spacing: -0.018em;
  margin-bottom: 8px;
}

.section-note { color: var(--faint); font-size: var(--t-small); margin: 0 0 34px; }
.section-title + .people-grid,
.section-title + .faculty,
.section-title + .pub-list,
.section-title + .card-list,
.section-title + .alumni-list,
.section-title + .video-grid { margin-top: 30px; }

.page-title {
  font-size: var(--t-title); font-weight: 700;
  letter-spacing: -0.024em; line-height: 1.06;
  margin-bottom: 16px;
}
.page-intro { margin: 0 0 76px; color: var(--muted); font-size: 19px; line-height: 1.5; }

/* --------------------------------------------------------- publications */

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

.pub {
  display: grid;
  grid-template-columns: 220px 1fr;
  align-items: start;
  gap: 30px;
  padding: 0 0 46px;      /* space between entries instead of a rule */
}
.pub:last-child { padding-bottom: 0; }

.pub-thumb {
  width: 220px;
  align-self: center;     /* equal space above and below, whatever its height */
  background: var(--bg-soft);
  border-radius: var(--radius-sm);
}
img.pub-thumb { height: auto; }
div.pub-thumb { aspect-ratio: 4 / 3; }   /* placeholder for a paper with no figure */

.pub-title {
  font-size: var(--t-item); font-weight: 600;
  letter-spacing: -0.014em; line-height: 1.3; margin: 0 0 8px;
}
.pub-authors { font-size: var(--t-small); color: var(--muted); margin: 0 0 6px; line-height: 1.5; }
.pub-authors .me { color: var(--ink); font-weight: 600; }
.pub-venue { font-size: var(--t-small); color: var(--ink); font-weight: 600; margin: 0; }
.pub-award {
  display: inline-block; margin-left: 10px;
  font-size: var(--t-meta); font-weight: 600; color: var(--accent);
}

.pub-links { display: flex; flex-wrap: wrap; gap: 18px; margin-top: 12px; }
.pub-links a { font-size: var(--t-small); color: var(--muted); }
.pub-links a:hover { color: var(--accent); }

/* -------------------------------------------------------------- people */

.faculty { display: flex; gap: 34px; align-items: flex-start; }
.faculty img {
  width: 190px; aspect-ratio: 1; object-fit: cover;
  border-radius: 20%; flex: none;
}
.faculty h3 { font-size: 23px; font-weight: 600; letter-spacing: -0.016em; margin-bottom: 4px; }
.faculty .person-role { font-size: var(--t-small); margin-bottom: 14px; }
.faculty p { margin: 0 0 12px; color: var(--muted); }

.people-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(132px, 1fr));
  gap: 38px 24px;
}

/* grid cards centre under the portrait; the faculty block stays left-aligned */
.member { text-align: center; }
.member img {
  width: 100%; aspect-ratio: 1; object-fit: cover;
  border-radius: 20%; background: var(--bg-soft);
  margin-bottom: 14px;
  transition: transform .25s ease;
}
.member a:hover img { transform: scale(1.03); }
.member h3 { font-size: var(--t-small); font-weight: 600; letter-spacing: -0.008em; margin-bottom: 2px; }
.member .person-social { justify-content: center; }

.person-role { font-size: var(--t-meta); color: var(--muted); margin: 0; line-height: 1.4; }
/* one step fainter than the role, so the card still reads name-first */
.person-start { font-size: var(--t-meta); color: var(--faint); margin: 3px 0 0; line-height: 1.4; }

/* three or four links do not fit one 132px card; without wrapping they spill
   into the neighbouring card and read as one run-on list */
.person-social { display: flex; flex-wrap: wrap; gap: 6px 11px; margin-top: 7px; }
.person-social a { font-size: var(--t-meta); color: var(--faint); }
.person-social a:hover { color: var(--accent); }

/* alumni as a compact reading list, not a photo wall */
.alumni-list { list-style: none; margin: 0; padding: 0; columns: 2; column-gap: 52px; }
.alumni-list li {
  break-inside: avoid; padding: 9px 0;
  font-size: var(--t-small); line-height: 1.45;
}
.alumni-list .person-role { display: inline; font-size: var(--t-small); }
.alumni-list .person-role::before { content: " \2014 "; }

/* ----------------------------------------------------------- code/video */

.card-list { list-style: none; margin: 0; padding: 0; }
.card-list li { padding: 0 0 26px; }
.card-list li:last-child { padding-bottom: 0; }
.card-list h3 { font-size: var(--t-item); font-weight: 600; letter-spacing: -0.012em; margin-bottom: 5px; }
.card-list p { margin: 0; font-size: var(--t-small); color: var(--muted); }

.video-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(330px, 1fr)); gap: 32px; }
.video-grid figure { margin: 0; }
.video-grid .frame {
  position: relative; padding-bottom: 56.25%; height: 0;
  border-radius: var(--radius-sm); overflow: hidden; background: var(--bg-soft);
}
.video-grid iframe { position: absolute; inset: 0; width: 100%; height: 100%; border: 0; }
.video-grid figcaption { margin-top: 12px; font-size: var(--t-small); color: var(--ink); font-weight: 600; }
.video-grid figcaption span { display: block; font-weight: 400; color: var(--faint); font-size: var(--t-meta); }

/* --------------------------------------------------------------- join */

.opening { padding: 0 0 44px; }
.opening:last-of-type { padding-bottom: 0; }
.opening h3 { font-size: var(--t-item); font-weight: 600; letter-spacing: -0.012em; margin-bottom: 8px; }
.opening p { margin: 0 0 10px; color: var(--muted); }

.opening-link { margin: 14px 0 0; font-weight: 600; font-size: var(--t-body); }
.opening-link a::after { content: " \2197"; color: var(--faint); font-weight: 400; }

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

.site-footer {
  padding: 0 0 56px;
  font-size: var(--t-meta); color: var(--faint);
}
.site-footer a { color: var(--faint); }
.site-footer a:hover { color: var(--ink); }
.site-footer p { margin: 0; }

/* --------------------------------------------------------- responsive */

@media (max-width: 860px) {
  .hero { flex-direction: column; gap: 32px; }
  .hero-logo { flex: none; width: 280px; align-self: center; margin-top: 0; }
  .hero-figure { margin-top: 48px; }
  .faculty { flex-direction: column; gap: 20px; }
  .faculty img { width: 160px; }
  .alumni-list { columns: 1; }
  .pub { grid-template-columns: 170px 1fr; gap: 24px; }
  .pub-thumb { width: 170px; }
}

@media (max-width: 600px) {
  :root { --t-section: 23px; --t-item: 18px; --t-body: 16.5px; }
  main { padding-top: 44px; padding-bottom: 80px; }
  .section { margin-top: 62px; }
  .page-intro { margin-bottom: 52px; font-size: var(--t-body); }
  .hero .lede { font-size: 19px; }
  .site-header nav { gap: 18px; }
  .pub { grid-template-columns: 110px 1fr; gap: 18px; padding-bottom: 38px; }
  .pub-thumb { width: 110px; }
  .people-grid { grid-template-columns: repeat(auto-fill, minmax(112px, 1fr)); gap: 30px 18px; }
}

@media (max-width: 380px) {
  .site-header nav { gap: 13px; }
  .site-header nav a, .brand { font-size: 13.5px; }
}

@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; }
}

@media print {
  .site-header, .skip-link { display: none; }
  main { padding-top: 0; }
}