:root {
  --ink: #10202f;
  --muted: #5c6c78;
  --paper: #f7f5ef;
  --panel: #ffffff;
  --accent: #ff6b35;
  --accent-2: #0a7b83;
  --line: #dbe2e7;
  --shadow: 0 24px 70px rgba(16, 32, 47, 0.12);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.65;
}

a { color: inherit; }
.skip-link {
  position: fixed;
  left: 1rem;
  top: -4rem;
  z-index: 100;
  background: #fff;
  padding: .75rem 1rem;
  border-radius: .5rem;
}
.skip-link:focus { top: 1rem; }

.hero {
  min-height: 78vh;
  display: grid;
  grid-template-rows: auto 1fr;
  background:
    radial-gradient(circle at 15% 20%, rgba(255,107,53,.25), transparent 25%),
    radial-gradient(circle at 85% 30%, rgba(10,123,131,.28), transparent 30%),
    #10202f;
  color: white;
}
.topbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1.2rem clamp(1rem, 4vw, 4rem);
  border-bottom: 1px solid rgba(255,255,255,.15);
}
.brand { font-weight: 800; text-decoration: none; }
.nav-links { display: flex; gap: 1rem; flex-wrap: wrap; }
.nav-links a { text-decoration: none; opacity: .82; }
.nav-links a:hover { opacity: 1; }
.hero-copy {
  width: min(900px, calc(100% - 2rem));
  margin: auto;
  padding: 5rem 0 7rem;
}
.eyebrow, .section-kicker {
  text-transform: uppercase;
  letter-spacing: .15em;
  font-size: .78rem;
  font-weight: 800;
}
.hero h1 {
  margin: .25rem 0 1rem;
  font-size: clamp(2.8rem, 7.2vw, 6.4rem);
  line-height: .92;
  max-width: 12ch;
}
.hero h1 span { display: block; }
.hero h1 span:nth-child(2) { color: var(--accent); }
.lede { max-width: 58ch; font-size: 1.25rem; color: rgba(255,255,255,.78); }
.button {
  display: inline-block;
  margin-top: 1rem;
  padding: .9rem 1.15rem;
  border-radius: 999px;
  background: var(--accent);
  color: white;
  text-decoration: none;
  font-weight: 800;
  border: 0;
  cursor: pointer;
}
.button.secondary { background: var(--ink); }

main {
  display: grid;
  grid-template-columns: minmax(320px, .8fr) minmax(0, 1.4fr);
  gap: clamp(2rem, 5vw, 6rem);
  width: min(1400px, calc(100% - 2rem));
  margin: 0 auto;
}
.protocol-stage { position: relative; }
.packet-panel {
  position: sticky;
  top: 1.5rem;
  min-height: calc(100vh - 3rem);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 2rem;
}
.layer-label {
  margin-bottom: 1rem;
  font-weight: 900;
  letter-spacing: .08em;
  text-transform: uppercase;
}
.packet {
  width: min(100%, 520px);
  background: white;
  border: 3px solid var(--ink);
  border-radius: 1rem;
  overflow: hidden;
  box-shadow: var(--shadow);
  transition: transform .5s ease;
}
.header, .trailer, .payload {
  padding: 1rem;
  border-bottom: 2px solid var(--ink);
  font-weight: 800;
  transition: all .45s ease;
}
.ethernet { background: #f9c74f; }
.ip { background: #90be6d; }
.tcp { background: #4d9de0; color: white; }
.payload { background: white; display: grid; gap: .25rem; }
.payload span { color: var(--muted); font-weight: 500; }
.trailer { background: #f9844a; border-bottom: 0; }
.packet .header, .packet .trailer { max-height: 0; opacity: 0; padding-block: 0; border-width: 0; }
.packet.transport .tcp,
.packet.network .tcp, .packet.network .ip,
.packet.link .tcp, .packet.link .ip, .packet.link .ethernet, .packet.link .trailer,
.packet.physical .tcp, .packet.physical .ip, .packet.physical .ethernet, .packet.physical .trailer {
  max-height: 100px;
  opacity: 1;
  padding: 1rem;
  border-width: 2px;
}
.packet.physical { transform: scale(.93); }
.bits {
  margin-top: 1.5rem;
  font-family: "SFMono-Regular", Consolas, monospace;
  color: var(--accent-2);
  opacity: 0;
  transform: translateY(8px);
  transition: .4s ease;
  text-align: center;
}
.bits.visible { opacity: 1; transform: translateY(0); }
.packet-note { color: var(--muted); text-align: center; }

.content-column { padding: 8rem 0; }
.syllabus-section, .arrival {
  min-height: 88vh;
  padding: 4rem 0;
  border-bottom: 1px solid var(--line);
  scroll-margin-top: 2rem;
}
.syllabus-section h2, .arrival h2 {
  margin: .2rem 0 1rem;
  font-size: clamp(2.2rem, 5vw, 4.8rem);
  line-height: 1;
  max-width: 12ch;
}
.syllabus-section h3 { margin-top: 2rem; }
.syllabus-section p, .syllabus-section li, .arrival p { font-size: 1.05rem; }
.info-grid, .grade-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0,1fr));
  gap: 1rem;
  margin: 2rem 0;
}
.info-grid article, .grade-grid article, .protocol-card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 1rem;
  padding: 1.25rem;
}
.info-grid h3, .grade-grid h3 { margin: 0 0 .3rem; }
.protocol-card { display: grid; gap: .8rem; }
.protocol-card div { display: flex; justify-content: space-between; gap: 2rem; border-bottom: 1px dashed var(--line); padding-bottom: .6rem; }
.protocol-card div:last-child { border-bottom: 0; }
.protocol-card span { color: var(--muted); }
.route-map { margin: 2rem 0; }
.route-stop {
  padding: 1rem 1.1rem;
  margin-bottom: .8rem;
  border-left: 4px solid var(--accent-2);
  border-radius: 0 .8rem .8rem 0;
  background: rgba(255,255,255,.72);
}
.route-stop small { display: block; color: var(--muted); }
.table-wrap { overflow-x: auto; }
table { width: 100%; border-collapse: collapse; background: white; }
th, td { text-align: left; padding: .9rem; border-bottom: 1px solid var(--line); }
th { background: #edf2f4; }
.grade-grid article span { font-size: 2rem; font-weight: 900; color: var(--accent-2); }
.policy-list details { background: white; border: 1px solid var(--line); border-radius: .8rem; padding: 1rem 1.1rem; margin-bottom: .8rem; }
.policy-list summary { cursor: pointer; font-weight: 900; }
.arrival { min-height: 65vh; }

footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  padding: 2rem clamp(1rem, 4vw, 4rem);
  background: var(--ink);
  color: white;
}
footer button { padding: .75rem 1rem; border-radius: 999px; border: 0; font-weight: 800; cursor: pointer; }

@media (max-width: 900px) {
  main { display: block; }
  .protocol-stage { height: 48vh; }
  .packet-panel { min-height: 48vh; top: 0; background: rgba(247,245,239,.96); z-index: 5; padding: 1rem; }
  .packet { width: min(92vw, 520px); }
  .content-column { padding-top: 1rem; }
  .info-grid, .grade-grid { grid-template-columns: 1fr; }
}

@media (max-width: 640px) {
  .nav-links { display: none; }
  .hero { min-height: 68vh; }
  .hero-copy { padding: 4rem 0; }
  .protocol-card div { display: grid; gap: .1rem; }
  footer { display: grid; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { transition: none !important; animation: none !important; }
}

@media print {
  .hero, .protocol-stage, footer button, .nav-links { display: none !important; }
  body { background: white; font-size: 11pt; }
  main { display: block; width: 100%; }
  .content-column { padding: 0; }
  .syllabus-section, .arrival { min-height: auto; break-inside: avoid; padding: 1.2rem 0; }
  .syllabus-section h2, .arrival h2 { font-size: 24pt; }
  details { break-inside: avoid; }
  footer { display: block; background: white; color: black; padding: 1rem 0; }
}

/* End-to-end physical transmission */
.transmission {
  width: min(100%, 560px);
  display: grid;
  grid-template-columns: 72px minmax(120px, 1fr) 72px;
  align-items: end;
  gap: .65rem;
  margin-top: 1.5rem;
  opacity: 0;
  max-height: 0;
  overflow: hidden;
  transform: translateY(10px);
  transition: opacity .4s ease, transform .4s ease, max-height .4s ease;
}
.packet-panel.transmitting .transmission,
.packet-panel.arrived .transmission {
  opacity: 1;
  max-height: 190px;
  overflow: visible;
  transform: translateY(0);
}
.endpoint { text-align: center; color: var(--muted); font-weight: 800; }
.computer-screen {
  width: 62px;
  height: 48px;
  margin: 0 auto;
  border: 4px solid var(--ink);
  border-radius: .5rem;
  background: #e8f7f8;
  display: grid;
  place-items: center;
  box-shadow: inset 0 0 0 3px white;
}
.computer-screen span { font-size: .8rem; font-weight: 900; color: var(--accent-2); }
.computer-base {
  width: 42px;
  height: 8px;
  margin: 3px auto 5px;
  border-radius: 0 0 8px 8px;
  background: var(--ink);
}
.medium { position: relative; height: 82px; min-width: 0; }
.wire {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 25px;
  height: 7px;
  border-radius: 999px;
  background: repeating-linear-gradient(90deg, var(--accent-2) 0 18px, #84c9cd 18px 30px);
  box-shadow: 0 0 0 3px white, 0 0 0 4px var(--line);
}
.signal-bits {
  position: absolute;
  top: 0;
  left: 50%;
  width: max-content;
  max-width: 100%;
  transform: translateX(-50%);
  overflow: hidden;
  white-space: nowrap;
  font: 700 .67rem/1 "SFMono-Regular", Consolas, monospace;
  color: var(--accent-2);
  opacity: .75;
}
.mini-packet {
  position: absolute;
  left: -2px;
  bottom: 14px;
  z-index: 2;
  width: 43px;
  height: 29px;
  display: grid;
  grid-template-columns: 8px 8px 8px 1fr;
  border: 2px solid var(--ink);
  border-radius: .35rem;
  overflow: hidden;
  background: white;
  box-shadow: 0 5px 12px rgba(16,32,47,.25);
}
.mini-packet i:nth-child(1) { background: #f9c74f; }
.mini-packet i:nth-child(2) { background: #90be6d; }
.mini-packet i:nth-child(3) { background: #4d9de0; }
.mini-packet i:nth-child(4) { background: white; }
.packet-panel.transmitting .mini-packet,
.packet-panel.arrived .mini-packet {
  transition: opacity .25s ease;
}
.packet-panel.arrived .mini-packet {
  opacity: .35;
}
.packet-panel.transmitting #packet {
  transform: scale(.28) translateY(26px);
  opacity: 0;
  pointer-events: none;
  max-height: 0;
}
.packet-panel.arrived #packet {
  transform: scale(1);
  opacity: 1;
  max-height: 520px;
  transition: none;
  animation: received-packet .6s .18s cubic-bezier(.2,.8,.2,1) both;
}
/* At the receiver, reveal the complete frame as one object. Without this,
   each header's max-height transition runs after the outer scale animation,
   which looks like a second expansion. */
.packet-panel.arrived #packet .header,
.packet-panel.arrived #packet .trailer,
.packet-panel.arrived #packet .payload {
  transition: none;
}
.packet-panel.arrived .destination-endpoint .computer-screen {
  animation: destination-glow 1.3s ease-in-out infinite alternate;
}
@keyframes received-packet {
  from { transform: scale(.5) translateX(35%); opacity: 0; }
  to { transform: scale(1) translateX(0); opacity: 1; }
}
@keyframes destination-glow {
  to { background: #c9f3e8; box-shadow: inset 0 0 0 3px white, 0 0 22px rgba(10,123,131,.38); }
}
@media (max-width: 520px) {
  .hero h1 { font-size: clamp(2.65rem, 15vw, 4.4rem); max-width: 11ch; }
  .transmission { grid-template-columns: 54px minmax(90px, 1fr) 54px; gap: .35rem; }
  .computer-screen { width: 48px; height: 39px; }
  .computer-base { width: 33px; }
  .signal-bits { font-size: .52rem; }
}
@media print {
  .transmission { display: none !important; }
}

/* Collapsible semester schedule */
.week-list {
  display: grid;
  gap: .8rem;
  margin-top: 2rem;
}

.week-card {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 1rem;
  overflow: hidden;
  box-shadow: 0 8px 24px rgba(15, 23, 42, .05);
}

.week-card summary {
  display: grid;
  grid-template-columns: 7rem 1fr;
  gap: 1rem;
  align-items: center;
  cursor: pointer;
  list-style: none;
  padding: 1rem 1.15rem;
  font-weight: 750;
}

.week-card summary::-webkit-details-marker { display: none; }

.week-card summary::after {
  content: "+";
  grid-column: 3;
  font-size: 1.35rem;
  line-height: 1;
  transition: transform .2s ease;
}

.week-card[open] summary::after { transform: rotate(45deg); }
.week-card summary span { color: var(--ink); }
.week-card summary small { color: var(--muted); font-weight: 600; }

.week-body {
  border-top: 1px solid var(--line);
  padding: .45rem 1.15rem .9rem;
}

.week-body p {
  display: grid;
  grid-template-columns: 7rem 6.5rem 1fr;
  gap: .8rem;
  align-items: baseline;
  margin: 0;
  padding: .8rem 0;
  border-bottom: 1px dashed var(--line);
}

.week-body p:last-child { border-bottom: 0; }
.week-body time { color: var(--muted); font-variant-numeric: tabular-nums; }
.week-body strong { color: var(--ink); }
.week-body .special,
.week-body .calendar-note {
  grid-template-columns: 7rem minmax(0, 1fr);
  border-radius: .65rem;
  margin-top: .35rem;
  padding: .75rem .8rem;
  border-bottom: 0;
}

.week-body .special strong,
.week-body .calendar-note strong {
  white-space: nowrap;
}

.week-body .calendar-note:not(:has(time)) strong {
  grid-column: 1 / -1;
}
.week-body .exam { background: #fff4e8; }
.week-body .no-class { background: #eef6ff; }
.week-body .tba { background: #f5f2ff; }
.week-body .calendar-note { background: #f7f8fa; color: var(--muted); }

@media (max-width: 720px) {
  .week-card summary { grid-template-columns: 5.5rem 1fr; gap: .6rem; }
  .week-card summary::after { grid-column: 3; }
  .week-body p { grid-template-columns: 1fr; gap: .2rem; }
  .week-body .special,
  .week-body .calendar-note { grid-template-columns: auto minmax(0, 1fr); }
  .week-body .special strong,
  .week-body .calendar-note strong { white-space: normal; }
}

@media print {
  .week-card { break-inside: avoid; }
  .week-card > .week-body { display: block !important; }
  .week-card summary::after { display: none; }
}

/* v7 refinements */
.hero h1 span:nth-child(3) {
  white-space: nowrap;
  font-size: .78em;
  letter-spacing: -.035em;
}

/* During launch, the full frame shrinks first. The miniature frame then
   takes over and moves across the link according to scroll position. */
.packet-panel.transmitting #packet {
  transform: translateY(calc(26px * var(--shrink, 1))) scale(calc(1 - .72 * var(--shrink, 1)));
  opacity: calc(1 - var(--shrink, 1));
  max-height: calc(520px * (1 - var(--shrink, 1)));
  transition: none;
}
.packet-panel.transmitting .mini-packet {
  opacity: var(--mini-visible, 1);
  transition: none;
}

@media (max-width: 720px) {
  .hero h1 span:nth-child(3) {
    font-size: .58em;
    letter-spacing: -.045em;
  }
}

/* Course materials */
.materials-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
  margin: 1.25rem 0 2rem;
}
.materials-grid article {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 1rem;
  padding: 1.25rem;
}
.materials-grid h4 {
  margin: .15rem 0 .7rem;
  font-size: 1.15rem;
}
.materials-grid p {
  font-size: .98rem;
}
.material-icon {
  margin: 0;
  font-size: 1.65rem !important;
}
.materials-grid a {
  color: var(--accent-2);
  font-weight: 800;
}
@media (max-width: 900px) {
  .materials-grid { grid-template-columns: 1fr; }
}

/* v9 content and motion refinements */
.hero h1 {
  max-width: 15ch;
  font-size: clamp(2.55rem, 6.3vw, 5.8rem);
  line-height: .96;
}
.hero h1 span {
  display: block;
  font-size: 1em !important;
  letter-spacing: -.045em !important;
  white-space: nowrap;
}
.hero h1 span:nth-child(2) { color: var(--accent); }

.packet {
  transition: transform .65s cubic-bezier(.16,1,.3,1), opacity .45s ease;
}
.header, .trailer, .payload {
  transition: max-height .62s cubic-bezier(.16,1,.3,1), opacity .34s ease, padding .62s cubic-bezier(.16,1,.3,1), border-width .34s ease;
}
.packet-panel.transmitting .transmission,
.packet-panel.arrived .transmission {
  transition: opacity .58s ease, transform .7s cubic-bezier(.16,1,.3,1), max-height .5s ease;
}

.final-note {
  background: rgba(10,123,131,.08);
  border-left: 4px solid var(--accent-2);
  border-radius: 0 .9rem .9rem 0;
  padding: 1rem 1.15rem;
  margin-top: 1rem;
}

/* Router waypoints in the physical-layer journey */
.router {
  --router-glow: 0;
  position: absolute;
  bottom: 0;
  z-index: 1;
  width: 64px;
  transform: translateX(-50%);
  text-align: center;
  color: var(--muted);
  font-weight: 800;
  pointer-events: none;
}
.router-one { left: 33.333%; }
.router-two { left: 66.666%; }
.router-body {
  position: relative;
  width: 48px;
  height: 28px;
  margin: 0 auto 4px;
  border: 3px solid var(--ink);
  border-radius: .45rem;
  background: #e8f7f8;
  box-shadow:
    inset 0 0 0 2px white,
    0 0 calc(4px + 18px * var(--router-glow)) rgba(10,123,131,.38);
  transition: background .12s linear, box-shadow .12s linear, transform .12s linear;
  transform: translateY(calc(-2px * var(--router-glow))) scale(calc(1 + .05 * var(--router-glow)));
}
.router-body::before,
.router-body::after {
  content: "";
  position: absolute;
  top: 50%;
  width: 7px;
  height: 7px;
  margin-top: -3.5px;
  border-radius: 50%;
  background: var(--accent-2);
  opacity: calc(.35 + .65 * var(--router-glow));
}
.router-body::before { left: 7px; }
.router-body::after { right: 7px; }
.router-body i {
  position: absolute;
  bottom: 4px;
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: #90be6d;
  opacity: calc(.35 + .65 * var(--router-glow));
}
.router-body i:nth-child(1) { left: 14px; }
.router-body i:nth-child(2) { left: 22px; }
.router-body i:nth-child(3) { left: 30px; }
.router small { font-size: .6rem; white-space: nowrap; }

@media (max-width: 520px) {
  .router { width: 48px; }
  .router-body { width: 38px; height: 24px; }
  .router-body i:nth-child(1) { left: 10px; }
  .router-body i:nth-child(2) { left: 17px; }
  .router-body i:nth-child(3) { left: 24px; }
  .router small { font-size: .5rem; }
}