/* =========================================================================
   Human Perception of Whole-Body Robot Motion — course project page
   ========================================================================= */

:root {
  --bg: #ffffff;
  --bg-soft: #f5f6f8;
  --text: #1c2026;
  --text-2: #424955;
  --text-3: #666d7a;
  --line: #e1e4e9;
  --navy: #1b2a4a;
  --link: #1f5fa8;

  /* method colours, matching the labels in the comparison video */
  --warp: #2e75b6;
  --mink: #b9540f;

  --serif: "Source Serif 4", "Iowan Old Style", "Palatino Linotype", Georgia, serif;
  --sans: "Source Sans 3", system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;

  --wrap: 960px;
  --gutter: clamp(16px, 4vw, 32px);
  --shadow: 0 1px 2px rgba(16, 24, 40, 0.04), 0 6px 18px rgba(16, 24, 40, 0.06);
}

/* ---------- base ---------- */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; color-scheme: light; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 400 18px/1.65 var(--sans);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
img, video, svg, picture { display: block; max-width: 100%; }
a { color: var(--link); text-underline-offset: 3px; }
a:hover { text-decoration-thickness: 2px; }
b, strong { font-weight: 600; }
:focus-visible { outline: 2px solid var(--link); outline-offset: 3px; border-radius: 4px; }

.wrap { width: min(100% - 2 * var(--gutter), var(--wrap)); margin-inline: auto; }
.nowrap { white-space: nowrap; }

.skip-link {
  position: absolute; left: 12px; top: -60px; z-index: 10;
  padding: 8px 14px; border-radius: 8px;
  background: var(--navy); color: #fff; font-weight: 600; text-decoration: none;
}
.skip-link:focus { top: 12px; }

/* ---------- title block ---------- */
.masthead { padding: clamp(56px, 9vw, 104px) 0 clamp(44px, 6vw, 68px); text-align: center; }
.course {
  margin: 0 0 22px;
  font-size: 15px; font-weight: 600; letter-spacing: 0.08em; text-transform: uppercase;
  color: var(--text-3);
}
.course span { white-space: nowrap; }
h1 {
  max-width: 780px; margin: 0 auto 14px;
  font: 600 clamp(32px, 5.2vw, 54px)/1.14 var(--serif);
  letter-spacing: -0.012em;
  text-wrap: balance;
}
.subtitle {
  margin: 0 0 30px;
  font: 400 clamp(19px, 2.4vw, 26px)/1.35 var(--serif);
  color: var(--text-2);
}
.affil { margin: 0 0 30px; font-size: 16.5px; color: var(--text-3); }

.links { display: flex; flex-wrap: wrap; justify-content: center; gap: 10px; }
.btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 8px 18px; border-radius: 999px;
  background: #262b33; color: #fff;
  font-size: 16px; font-weight: 600; text-decoration: none;
  transition: background-color 0.15s ease;
}
.btn:hover { background: var(--navy); }
.btn svg { width: 16px; height: 16px; flex: none; }

/* ---------- sections ---------- */
.section { padding: clamp(48px, 7vw, 84px) 0; }
.section-soft { background: var(--bg-soft); }
h2 {
  margin: 0 0 14px;
  font: 600 clamp(26px, 3.3vw, 34px)/1.2 var(--serif);
  letter-spacing: -0.008em;
  text-align: center;
}
.lead {
  max-width: 740px; margin: 0 auto clamp(26px, 3.5vw, 36px);
  font-size: clamp(17px, 1.8vw, 19.5px);
  color: var(--text-2);
  text-align: center;
  text-wrap: pretty;
}

/* ---------- cards ---------- */
.card {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 14px;
  box-shadow: var(--shadow);
  padding: clamp(22px, 3vw, 30px) clamp(22px, 3.4vw, 34px);
}
.card p { margin: 0; font-size: clamp(17px, 1.8vw, 19px); line-height: 1.6; color: var(--text-2); }
.card b { color: var(--navy); }
.card .kicker {
  margin: 0 0 10px;
  font-size: 13.5px; font-weight: 700; line-height: 1.2; letter-spacing: 0.09em; text-transform: uppercase;
  color: var(--mink);
}

/* ---------- sliding cards: one per page; swipe, arrows, dots or arrow keys ---------- */
.slider {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  align-items: center;
  column-gap: 10px;
  max-width: 880px; margin: clamp(22px, 3vw, 30px) auto 0;
}
.slider-track {
  grid-column: 2;
  display: flex;
  margin: 0; padding: 0; list-style: none;
  overflow-x: auto;
  scroll-snap-type: x mandatory;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: none;
  border-radius: 16px;
}
.slider-track::-webkit-scrollbar { display: none; }
.slide {
  flex: 0 0 100%;
  display: flex;
  padding: 6px 12px 24px; /* room for the card shadow inside the scroll container */
  scroll-snap-align: center;
}
.slide .card { flex: 1; display: flex; flex-direction: column; justify-content: center; }

.slider-arrow {
  display: grid; place-items: center;
  width: 44px; height: 44px; margin-bottom: 18px; padding: 0;
  border: 1px solid rgba(27, 42, 74, 0.18); border-radius: 50%;
  background: #fff; color: var(--navy);
  box-shadow: 0 2px 8px rgba(16, 24, 40, 0.1);
  cursor: pointer;
  transition: background-color 0.15s ease, color 0.15s ease, opacity 0.15s ease;
}
.slider-arrow svg { width: 16px; height: 16px; }
.slider-arrow:hover { background: var(--navy); color: #fff; }
.slider-arrow[aria-disabled="true"] { opacity: 0.3; cursor: default; background: #fff; color: var(--navy); }

.slider-dots { grid-column: 1 / -1; display: flex; justify-content: center; gap: 2px; }
.slider-dots button {
  position: relative;
  width: 20px; height: 24px; padding: 0; border: 0; background: none;
  cursor: pointer;
  transition: width 0.2s ease;
}
.slider-dots button::before {
  content: ""; position: absolute; left: 6px; right: 6px; top: 8px; height: 8px;
  border-radius: 999px; background: #cdd2da;
  transition: background-color 0.2s ease;
}
.slider-dots button[aria-current="true"] { width: 36px; }
.slider-dots button[aria-current="true"]::before { background: var(--navy); }

/* without JavaScript the cards simply stack */
html:not(.js) .slider { display: block; }
html:not(.js) .slider-track { display: block; overflow: visible; }
html:not(.js) .slide { padding-bottom: 10px; }
html:not(.js) .slider-arrow, html:not(.js) .slider-dots { display: none; }

/* ---------- figures ---------- */
.figure { margin: 0; }
.figure video {
  width: 100%; height: auto; aspect-ratio: 16 / 9;
  border: 1px solid var(--line); border-radius: 12px;
  background: #fafafa;
  box-shadow: var(--shadow);
}
figcaption {
  max-width: 780px; margin: 14px auto 0;
  font-size: 16px; line-height: 1.55;
  color: var(--text-3);
  text-align: center;
  text-wrap: pretty;
}
figcaption b { color: var(--text-2); }

/* ---------- method cards ---------- */
.methods { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin-top: clamp(30px, 4vw, 44px); }
.method { position: relative; overflow: hidden; }
.method::before { content: ""; position: absolute; inset: 0 0 auto; height: 3px; background: var(--mc); }
.method-warp { --mc: var(--warp); }
.method-mink { --mc: var(--mink); }
.method .kicker { color: var(--text-3); }
.method h3 { margin: 0 0 8px; font: 700 23px/1.2 var(--sans); color: var(--mc); }
.method p { font-size: 17px; }

/* ---------- robot platform ---------- */
.robot {
  display: grid;
  grid-template-columns: minmax(0, 360px) minmax(0, 1fr);
  grid-template-rows: auto 1fr;
  grid-template-areas: "photo intro" "photo specs";
  column-gap: clamp(32px, 6vw, 72px); row-gap: 18px;
  align-items: start;
}
.robot-intro { grid-area: intro; }
.robot-intro h2 { text-align: left; }
.robot-intro p { margin: 0; color: var(--text-2); }
.robot-intro b { color: var(--text); }

.robot-photo { grid-area: photo; margin: 0; }
.robot-frame {
  position: relative; overflow: hidden;
  border: 1px solid var(--line); border-radius: 12px;
  box-shadow: var(--shadow);
}
.robot-frame img { width: 100%; height: auto; }
.robot-photo figcaption { font-size: 15px; }

.marker {
  position: absolute; left: var(--x); top: var(--y);
  width: 24px; height: 24px; margin: -12px 0 0 -12px;
  border: 2px solid #fff; border-radius: 50%;
  background: var(--navy); color: #fff;
  font: 700 13px/20px var(--sans); text-align: center;
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.4);
  cursor: default;
  transition: background-color 0.15s ease, transform 0.15s ease;
}

.specs { grid-area: specs; margin: 0; padding: 0; list-style: none; }
.specs li {
  display: flex; align-items: flex-start; gap: 14px;
  margin-left: -12px; padding: 8px 12px;
  border-radius: 10px;
  transition: background-color 0.15s ease;
}
.specs .num {
  flex: none; width: 24px; height: 24px; margin-top: 2px;
  border-radius: 50%;
  background: var(--navy); color: #fff;
  font: 700 12.5px/24px var(--sans); text-align: center;
  transition: background-color 0.15s ease;
}
.specs strong { display: block; line-height: 1.4; }
.specs div span { display: block; font-size: 16.5px; line-height: 1.45; color: var(--text-3); }

/* hovering a list entry or a marker highlights its counterpart */
.specs li.is-on { background: rgba(46, 117, 182, 0.1); }
.specs li.is-on .num, .marker.is-on { background: var(--warp); }
.marker.is-on { transform: scale(1.2); }

/* ---------- footer ---------- */
.footer {
  padding: 34px 0 44px;
  border-top: 1px solid var(--line);
  font-size: 15.5px; line-height: 1.6;
  color: var(--text-3);
  text-align: center;
}
.footer p { max-width: 760px; margin: 0 auto 6px; }

/* ---------- responsive ---------- */
@media (max-width: 760px) {
  .methods { grid-template-columns: 1fr; gap: 16px; }

  .robot { grid-template-columns: minmax(0, 1fr); grid-template-rows: auto; grid-template-areas: "intro" "photo" "specs"; row-gap: 26px; }
  .robot-intro h2 { text-align: center; }
  .robot-photo { width: min(100%, 400px); margin-inline: auto; }
  .specs li { margin-left: 0; }
}

@media (max-width: 640px) {
  .course span { display: block; }
  .course .sep { display: none; }

  /* arrows move under the card, beside the dots */
  .slider { column-gap: 6px; }
  .slider-track { grid-column: 1 / -1; grid-row: 1; }
  .slide { padding: 6px 4px 20px; }
  .slider-prev { grid-column: 1; grid-row: 2; }
  .slider-dots { grid-column: 2; grid-row: 2; }
  .slider-next { grid-column: 3; grid-row: 2; }
  .slider-arrow { width: 40px; height: 40px; margin-bottom: 0; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { transition-duration: 0.01ms !important; }
}