/*
 * How Long Is a Billion? — styles
 * House style: white page, heavy black grotesque type, 2px ink borders,
 * chunky offset shadows and bright accent colours. No external fonts.
 */

:root {
  --bg: #ffffff;
  --text: #111111;
  --text-muted: #6b6b6b;
  --border: #111111;
  --accent: #ff4757;
  --accent-green: #2ed573;
  --accent-blue: #1e90ff;
  --accent-yellow: #ffa502;
  --accent-purple: #8e6cff;
  --night: #0c0e1f;
  --font-main: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --font-mono: "SF Mono", Monaco, "Cascadia Code", "Roboto Mono", Consolas, monospace;

  --spine-x: 78px;
  --read: 40%;
  --safe-t: env(safe-area-inset-top, 0px);
  --safe-r: env(safe-area-inset-right, 0px);
  --safe-b: env(safe-area-inset-bottom, 0px);
  --safe-l: env(safe-area-inset-left, 0px);
  --hud-space: 230px;
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  overflow-x: hidden;
  overflow-x: clip;
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  background: var(--bg);
}

body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-main);
  line-height: 1.45;
  overflow-x: hidden;
  overflow-x: clip;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  -webkit-tap-highlight-color: transparent;
}

a { color: inherit; }

:focus-visible {
  outline: 3px solid var(--accent-blue);
  outline-offset: 3px;
}

.visually-hidden {
  position: absolute !important;
  width: 1px; height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  white-space: nowrap;
}

.sprite { position: absolute; width: 0; height: 0; overflow: hidden; }

.skip-link {
  position: absolute;
  left: 12px; top: -60px;
  z-index: 100;
  background: var(--text); color: var(--bg);
  padding: 10px 14px; border-radius: 10px;
  font-weight: 800; text-decoration: none;
}
.skip-link:focus { top: calc(12px + var(--safe-t)); }

kbd {
  font-family: var(--font-mono);
  font-size: 0.85em;
  font-weight: 700;
  border: 2px solid var(--border);
  border-bottom-width: 3px;
  border-radius: 6px;
  padding: 0 6px;
  background: var(--bg);
}

/* ---------- Buttons ---------- */
.btn {
  font: inherit;
  font-weight: 800;
  color: var(--text);
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: 999px;
  box-shadow: 0 4px 0 var(--border);
  cursor: pointer;
  transition: transform 0.1s ease, box-shadow 0.1s ease, background 0.15s ease;
  touch-action: manipulation;
}
.btn:hover { transform: translateY(-2px); box-shadow: 0 6px 0 var(--border); }
.btn:active { transform: translateY(3px); box-shadow: 0 1px 0 var(--border); }

.btn--big {
  font-size: clamp(1.1rem, 3.6vw, 1.35rem);
  padding: 16px 30px;
  background: var(--text);
  color: var(--bg);
}
.btn--big:hover { background: #2a2a2a; }
.btn--light { background: var(--bg); color: var(--text); border-color: var(--bg); box-shadow: 0 4px 0 #8b8fb8; }
.btn--light:hover { background: #f2f2f7; box-shadow: 0 6px 0 #8b8fb8; }

.btn--small { font-size: 0.95rem; padding: 10px 14px; min-height: 44px; }
.btn--ghost { min-width: 48px; }
.btn--next {
  flex: 1;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  min-width: 0;
  background: var(--accent-yellow);
}
.btn--next #next-name { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.next__label { font-weight: 600; opacity: 0.75; }

/* ---------- Top bar ---------- */
.topbar {
  position: fixed;
  top: calc(10px + var(--safe-t));
  left: calc(10px + var(--safe-l));
  right: calc(10px + var(--safe-r));
  z-index: 50;
  display: flex;
  justify-content: space-between;
  pointer-events: none;
}
.pill {
  pointer-events: auto;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: 999px;
  box-shadow: 0 2px 0 var(--border);
  padding: 7px 14px;
  font-size: 0.85rem;
  font-weight: 800;
  text-decoration: none;
  min-height: 38px;
  transition: transform 0.15s ease, opacity 0.2s ease;
}
.pill:hover { transform: translateY(-2px); }
.pill__icon { width: 18px; height: 18px; }
.is-idle .pill--brand { opacity: 0; pointer-events: none; transform: translateY(-6px); }

/* ---------- Intro ---------- */
.intro {
  min-height: 100vh;
  min-height: 100svh;
  display: grid;
  place-items: center;
  text-align: center;
  padding: calc(70px + var(--safe-t)) calc(22px + var(--safe-r)) calc(60px + var(--safe-b)) calc(22px + var(--safe-l));
}
.intro__inner { max-width: 720px; }
.intro__glass {
  width: 76px; height: 76px;
  color: var(--text);
  margin-bottom: 18px;
  animation: flip 4.5s cubic-bezier(0.7, 0, 0.3, 1) infinite;
}
@keyframes flip {
  0%, 70% { transform: rotate(0deg); }
  85%, 100% { transform: rotate(180deg); }
}
.intro__kicker {
  font-size: 0.85rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--text-muted);
  margin-bottom: 12px;
}
.intro__title {
  text-wrap: balance;
  font-weight: 900;
  font-size: clamp(2.9rem, 11vw, 6.4rem);
  letter-spacing: -0.045em;
  line-height: 0.95;
  margin-bottom: 22px;
}
.hl {
  background: var(--accent-yellow);
  padding: 0 0.12em;
  border-radius: 0.12em;
  box-decoration-break: clone;
  -webkit-box-decoration-break: clone;
}
.intro__lede {
  font-size: clamp(1.05rem, 3.4vw, 1.3rem);
  color: #333;
  max-width: 34em;
  margin: 0 auto 28px;
}
.intro__keys { margin-top: 22px; font-size: 0.9rem; color: var(--text-muted); }
.noscript { margin-top: 24px; font-weight: 700; }

/* ---------- Timeline ---------- */
.timeline-wrap {
  position: relative;
  max-width: 820px;
  margin: 0 auto;
}
.timeline {
  position: relative;
  /* height set from JS, from the real time-to-pixel maths */
}
.timeline__spine { display: none; }
.timeline__ticks, .timeline__items {
  position: absolute;
  inset: 0;
  list-style: none;
}

/* Zone bands: a faint wash plus a coloured stripe and the ink spine */
.zone {
  position: absolute;
  /* full-bleed: bands run edge to edge, the ruler stays in the column */
  left: -100vw; right: -100vw;
}
.zone::before {
  content: "";
  position: absolute;
  top: 0; bottom: 0;
  left: calc(100vw + var(--spine-x) - 9px);
  width: 6px;
  border-radius: 3px;
  background: var(--zc, var(--text));
  opacity: 0.85;
}
.zone::after {
  content: "";
  position: absolute;
  top: 0; bottom: 0;
  left: calc(100vw + var(--spine-x) - 1.5px);
  width: 3px;
  background: var(--text);
}
.zone--blue   { --zc: var(--accent-blue); }
.zone--green  { --zc: var(--accent-green); }
.zone--yellow { --zc: var(--accent-yellow); }
.zone--red    { --zc: var(--accent); }
.zone--purple { --zc: var(--accent-purple); }
.zone--ink    { --zc: #9aa0ff; }

.zone--deep {
  background:
    radial-gradient(1.2px 1.2px at 12% 20%, rgba(255,255,255,0.8) 50%, transparent 52%) 0 0 / 230px 190px,
    radial-gradient(1px 1px at 70% 60%, rgba(255,255,255,0.6) 50%, transparent 52%) 0 0 / 170px 150px,
    radial-gradient(1.5px 1.5px at 40% 80%, rgba(255,255,255,0.7) 50%, transparent 52%) 0 0 / 310px 260px,
    linear-gradient(to bottom, var(--bg) 0%, var(--bg) 10%, #e9e8ff 24%, #3a3f7a 46%, #161a3a 62%, var(--night) 100%);
  background-repeat: repeat, repeat, repeat, no-repeat;
}
.zone--deep::after {
  background: linear-gradient(to bottom, var(--text) 0%, var(--text) 36%, #f4f4ff 52%, #f4f4ff 100%);
}

.zone--end { background: var(--night); }
.zone--end::before, .zone--end::after { display: none; }
.decade {
  position: absolute;
  left: -100vw; right: -100vw;
  pointer-events: none;
}
.decade--alt { background: rgba(120, 120, 200, 0.07); }

.tick {
  position: absolute;
  left: calc(var(--spine-x) - 9px);
  width: 9px;
  height: 0;
  border-top: 2px solid var(--text);
  opacity: 0.55;
}
.tick--major { left: calc(var(--spine-x) - 18px); width: 18px; opacity: 1; }
.tick__label {
  position: absolute;
  right: calc(100% + 6px);
  top: -0.7em;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 700;
  white-space: nowrap;
  color: var(--text);
  line-height: 1.2;
}
.tick--deep { border-top-color: currentColor; color: var(--text); }
.tick--deep .tick__label {
  background: var(--bg);
  border: 1.5px solid var(--border);
  border-radius: 6px;
  padding: 1px 5px;
  top: -0.85em;
  font-size: 0.66rem;
  left: auto;
}
.tick--deep.tick--major { width: 18px; }

/* entries */
.entry {
  position: absolute;
  left: 0; right: 0;
  height: 0;
}
.entry__dot {
  position: absolute;
  left: calc(var(--spine-x) - 8px);
  top: -8px;
  width: 16px; height: 16px;
  border-radius: 50%;
  background: var(--bg);
  border: 3px solid var(--text);
  z-index: 2;
  transition: background 0.2s ease, transform 0.2s ease;
}
.entry--banner .entry__dot { border-radius: 4px; transform: rotate(45deg); }
.is-reached .entry__dot { background: var(--accent); transform: scale(1.15); }
.entry--banner.is-reached .entry__dot { transform: rotate(45deg) scale(1.15); background: var(--accent-yellow); }

/* leader from a nudged card back to its true spot */
.entry::after {
  content: "";
  position: absolute;
  top: 0;
  left: calc(var(--spine-x) + 8px);
  width: 14px;
  height: 0;
  border-top: 2px solid var(--text);
}
.entry--nudged::after {
  height: calc(var(--nudge) + 22px);
  border-top: 2px dashed var(--text);
  border-left: 2px dashed var(--text);
  border-top-left-radius: 6px;
}
.entry--dark::after { border-color: #f4f4ff; }
.entry--dark .entry__dot { border-color: #f4f4ff; background: var(--night); }
.entry--dark.is-reached .entry__dot { background: var(--accent); }
.tick.is-dark { border-top-color: #f4f4ff; }

.card {
  position: absolute;
  top: 0;
  left: calc(var(--spine-x) + 22px);
  right: calc(12px + var(--safe-r));
  max-width: 540px;
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: 16px;
  box-shadow: 4px 4px 0 var(--border);
  padding: 14px 16px 12px;
  will-change: transform;
}
.card:focus { outline: none; }
.card:focus-visible, .card:focus { box-shadow: 4px 4px 0 var(--border), 0 0 0 4px var(--accent-blue); }
.card__head { display: flex; align-items: center; gap: 8px; margin-bottom: 6px; }
.card__icon { width: 22px; height: 22px; flex: none; }
.card__tag {
  font-size: 0.7rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--text-muted);
}
.card__title {
  font-size: clamp(1.15rem, 4.2vw, 1.45rem);
  font-weight: 900;
  letter-spacing: -0.02em;
  line-height: 1.15;
}
.card__figure {
  font-size: clamp(1.6rem, 6.5vw, 2.3rem);
  font-weight: 900;
  letter-spacing: -0.035em;
  line-height: 1.05;
  margin: 4px 0 6px;
  font-variant-numeric: tabular-nums;
}
.card__body { font-size: 0.98rem; color: #262626; margin-top: 4px; }
.card__source {
  margin-top: 10px;
  font-size: 0.75rem;
  color: var(--text-muted);
  overflow-wrap: anywhere;
}
.card__source a { font-weight: 700; color: var(--text); text-underline-offset: 2px; }
.card__ref { font-family: var(--font-mono); }

.card--aside {
  border-style: dashed;
  box-shadow: none;
  background: #fffdf6;
}
.card--aside .card__tag { color: #a05f00; }
.card--aside .card__title { font-size: clamp(1.05rem, 3.8vw, 1.25rem); }

.card--star { border-width: 3px; box-shadow: 6px 6px 0 var(--accent); }
.card--star .card__figure { color: var(--accent); font-size: clamp(2rem, 9vw, 3.1rem); }

.card--banner {
  max-width: 600px;
  border-width: 3px;
  box-shadow: 6px 6px 0 var(--border);
  background: var(--bg);
  overflow: hidden;
}
.card--banner::before {
  content: "";
  position: absolute;
  inset: 0 auto 0 0;
  width: 10px;
  background: var(--zc, var(--text));
}
.card--banner { padding-left: 24px; }
.card--blue   { --zc: var(--accent-blue); }
.card--green  { --zc: var(--accent-green); }
.card--yellow { --zc: var(--accent-yellow); }
.card--red    { --zc: var(--accent); }
.card--purple { --zc: var(--accent-purple); }
.card--ink    { --zc: #5b61d6; }
.card--banner .card__title { font-size: clamp(1.35rem, 5.4vw, 1.9rem); }
.card__scale {
  display: inline-block;
  margin-top: 10px;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  font-weight: 800;
  border: 2px solid var(--border);
  border-radius: 999px;
  padding: 3px 12px;
  background: var(--zc);
  color: var(--text);
}

@keyframes pop {
  0% { scale: 1; }
  40% { scale: 1.035; }
  100% { scale: 1; }
}
.is-reached .card--marker, .is-reached .card--banner { animation: pop 0.45s cubic-bezier(0.34, 1.56, 0.64, 1); }

/* ---------- Playhead ---------- */
.playhead {
  position: fixed;
  top: var(--read);
  left: 0; right: 0;
  height: 0;
  border-top: 2px dashed var(--accent);
  z-index: 30;
  pointer-events: none;
  transition: opacity 0.25s ease;
}
.playhead__tag {
  position: absolute;
  left: calc(6px + var(--safe-l));
  top: -22px;
  background: var(--accent);
  color: #fff;
  font-size: 0.62rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  padding: 2px 7px;
  border-radius: 999px;
}
.is-idle .playhead, .is-past .playhead { opacity: 0; }

/* ---------- HUD ---------- */
.hud {
  position: fixed;
  z-index: 40;
  left: calc(10px + var(--safe-l));
  right: calc(10px + var(--safe-r));
  bottom: calc(10px + var(--safe-b));
  max-width: 560px;
  margin: 0 auto;
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: 20px;
  box-shadow: 0 5px 0 var(--border);
  padding: 10px 12px 12px;
  transition: transform 0.35s cubic-bezier(0.34, 1.4, 0.64, 1), opacity 0.25s ease, visibility 0.35s;
}
.is-idle .hud, .is-past .hud { transform: translateY(calc(100% + 30px)); opacity: 0; visibility: hidden; }
.hud__row--top { display: flex; justify-content: space-between; align-items: center; gap: 8px; }
.hud__label {
  font-size: 0.68rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--text-muted);
}
.hud__scale {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 800;
  border: 2px solid var(--border);
  border-radius: 999px;
  padding: 1px 9px;
  white-space: nowrap;
  background: var(--accent-blue);
}
.hud__scale--blue { background: var(--accent-blue); color: #fff; }
.hud__scale--green { background: var(--accent-green); }
.hud__scale--yellow { background: var(--accent-yellow); }
.hud__scale--red { background: var(--accent); color: #fff; }
.hud__scale--purple { background: var(--accent-purple); color: #fff; }
.hud__scale--ink { background: var(--text); color: #fff; }
.hud__count {
  margin-top: 2px;
  font-weight: 900;
  font-size: clamp(1.7rem, 8vw, 2.4rem);
  letter-spacing: -0.04em;
  line-height: 1.05;
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.hud__unit { font-size: 0.5em; font-weight: 700; letter-spacing: -0.01em; color: var(--text-muted); }
.hud__human { font-weight: 800; font-size: 1rem; min-height: 1.45em; }
.hud__quip { font-size: 0.82rem; color: var(--text-muted); line-height: 1.3; margin-top: 1px; }
.hud__progress {
  height: 6px;
  border-radius: 3px;
  background: #ececec;
  overflow: hidden;
  margin: 8px 0 10px;
}
.hud__progress span {
  display: block;
  height: 100%;
  background: var(--text);
  transform-origin: 0 50%;
  transform: scaleX(0);
}
.hud__controls { display: flex; gap: 8px; }

/* ---------- Outro ---------- */
.outro {
  background: var(--night);
  color: #f4f4ff;
  text-align: center;
  padding: 90px calc(22px + var(--safe-r)) 90px calc(22px + var(--safe-l));
}
.outro__inner { max-width: 640px; margin: 0 auto; }
.outro__icon { width: 64px; height: 64px; margin-bottom: 16px; color: #c9c6ff; }
.outro__title { text-wrap: balance; font-size: clamp(2rem, 8vw, 3.6rem); font-weight: 900; letter-spacing: -0.04em; line-height: 1; margin-bottom: 18px; }
.outro__lede { font-size: 1.1rem; margin-bottom: 14px; }
.outro__stat { font-size: 0.95rem; color: #b9bbdd; margin-bottom: 28px; }

/* ---------- Sources ---------- */
.sources { padding: 70px calc(22px + var(--safe-r)) 40px calc(22px + var(--safe-l)); }
.sources:focus { outline: none; }
.sources__inner { max-width: 760px; margin: 0 auto; }
.sources h2 { font-size: clamp(1.8rem, 6vw, 2.6rem); font-weight: 900; letter-spacing: -0.03em; margin-bottom: 10px; }
.sources p { color: #333; margin-bottom: 18px; }
.sources__list { padding-left: 1.6em; display: grid; gap: 10px; }
.sources__list li { padding-left: 4px; }
.sources__list a { font-weight: 700; text-underline-offset: 2px; }
.sources__url { display: block; font-family: var(--font-mono); font-size: 0.72rem; color: var(--text-muted); overflow-wrap: anywhere; }
.sources__note { font-size: 0.9rem; color: var(--text-muted) !important; margin-top: 18px; }

.footer {
  text-align: center;
  font-size: 0.85rem;
  color: var(--text-muted);
  padding: 20px 22px calc(24px + var(--safe-b));
  border-top: 2px solid #eee;
}

/* ---------- Larger screens ---------- */
@media (min-width: 700px) {
  :root { --spine-x: 120px; --read: 42%; }
  .tick__label { font-size: 0.78rem; }
  .card { padding: 16px 20px 14px; }
}

@media (min-width: 1100px) {
  :root { --hud-space: 40px; --read: 45%; }
  .timeline-wrap { margin-left: max(24px, calc(50% - 560px)); margin-right: 400px; max-width: 720px; }
  .playhead { right: calc(max(24px, 50% - 560px) + 356px); }
  .card { max-width: 580px; }
  .hud {
    left: auto;
    right: max(24px, calc(50% - 560px));
    bottom: auto;
    top: 50%;
    width: 340px;
    transform: translateY(-50%);
    padding: 16px 16px 16px;
  }
  .is-idle .hud, .is-past .hud { transform: translate(calc(100% + 40px), -50%); }
  .hud__count { font-size: 2.3rem; }
  .hud__quip { font-size: 0.88rem; margin-top: 4px; }
}

/* Short landscape phones: keep the HUD compact */
@media (max-height: 520px) {
  .hud__quip, .hud__progress { display: none; }
  .hud__controls { margin-top: 6px; }
}

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

/* Landscape phones: tuck the HUD to the side so the timeline stays visible */
@media (max-height: 520px) and (min-width: 640px) {
  .hud { left: auto; right: calc(10px + var(--safe-r)); width: 300px; margin: 0; padding: 8px 10px 10px; }
  .hud__count { font-size: 1.6rem; }
  .timeline-wrap { margin-right: 320px; }
  .playhead { right: calc(320px + var(--safe-r)); }
}