:root {
  --bg: #121212; --ink: #f4f4f2; --muted: #c4c4bf; --faint: #9d9d98; --line: #f4f4f2;
  --spring: cubic-bezier(.42, 1.67, .21, .9);
  --ease: cubic-bezier(.2, 0, 0, 1);
  /* Type scale: every font-size uses one of these roles (line-height noted per role) */
  --text-caption: .8125rem;  /* 13px, 1.4: counters, sources, labels, menu */
  --text-label: .875rem;     /* 14px: topic marks, hints, text links */
  --text-ui: .9375rem;       /* 15px: buttons, secondary copy */
  --text-body: 1rem;         /* 16px, 1.5: descriptions, examples, credits */
  --text-lead: 1.125rem;     /* 18px, 1.45: intro lead */
  --text-question: 1.375rem; /* 22px, 1.4: quiz questions */
  --text-title: clamp(2rem, 8.6vw, 2.75rem);   /* 1.06: spark and About titles */
  --text-display: clamp(2.5rem, 11vw, 3.5rem); /* 1: intro title */
  --text-score: clamp(3.5rem, 18vw, 5rem);     /* 1: quiz score */
  color-scheme: dark;
  box-sizing: border-box;
  padding-top: env(safe-area-inset-top, 0px);
  padding-bottom: env(safe-area-inset-bottom, 0px);
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) { --bg: #121212; --ink: #f4f4f2; --muted: #c4c4bf; --faint: #9d9d98; --line: #f4f4f2; }
}
:root[data-theme="dark"] { --bg: #121212; --ink: #f4f4f2; --muted: #c4c4bf; --faint: #9d9d98; --line: #f4f4f2; }

*, *::before, *::after { box-sizing: border-box; }
html { height: 100%; background: var(--bg); scroll-padding-top: env(safe-area-inset-top, 0px); }
body {
  margin: 0; height: 100%; overflow: hidden; position: relative;
  background: var(--bg); color: var(--ink);
  font-family: "Roboto Flex", "Helvetica Neue", Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased; -moz-osx-font-smoothing: grayscale;
}

/* Drawing */
.stage { position: absolute; left: 0; right: 0; top: 0; height: 46%; display: grid; place-items: center; pointer-events: none; z-index: 0; }
.stage canvas { width: min(74vw, 38vh, 360px); aspect-ratio: 1; display: block; }

.count { position: absolute; left: 28px; top: 20px; z-index: 3; margin: 0; font-size: var(--text-caption); font-weight: 500; color: var(--faint); font-variant-numeric: tabular-nums; }
.count b { color: var(--ink); font-weight: 600; }

/* Vertical feed */
.feed {
  position: relative; z-index: 1; height: 100%; overflow-y: auto; overscroll-behavior: contain;
  scroll-snap-type: y mandatory; scrollbar-width: none; transition: opacity .25s var(--ease);
}
.feed::-webkit-scrollbar { display: none; }
.feed.fading { opacity: 0; }
.slide {
  height: 100%; scroll-snap-align: start; scroll-snap-stop: always;
  display: flex; flex-direction: column; justify-content: flex-end; padding-bottom: 96px;
}

/* Horizontal pages inside each slide: the idea, then examples. The next card peeks in. */
.hscroll {
  display: flex; align-items: flex-end; gap: 12px; overflow-x: auto; overflow-y: hidden; overscroll-behavior-x: contain;
  scroll-snap-type: x mandatory; padding: 0 28px 6px; scroll-padding: 0 28px; /* 6px below so the card's bottom border isn't clipped */ scrollbar-width: none;
}
.hscroll::-webkit-scrollbar { display: none; }
.hscroll::after { content: ""; flex: 0 0 16px; }
.page { flex: 0 0 calc(100% - 64px); max-width: 480px; min-width: 0; scroll-snap-align: start; }
.page > * { will-change: transform, opacity; }

.mark { margin: 0 0 12px; font-size: var(--text-label); font-weight: 600; font-stretch: 112%; letter-spacing: .01em; }
.dot { display: inline-block; width: 10px; height: 10px; border-radius: 50%; margin-right: 8px; vertical-align: 1px; }
.title {
  margin: 0 0 12px; font-weight: 700; font-size: var(--text-title); line-height: 1.06; letter-spacing: -0.025em; text-wrap: balance;
  font-variation-settings: "opsz" 144;
}
.desc { margin: 0 0 8px; font-size: var(--text-body); line-height: 1.5; color: var(--muted); max-width: 38ch; text-wrap: pretty; }
.source { margin: 0; font-size: var(--text-caption); line-height: 1.4; color: var(--faint); }
/* text-to-text: the idea's last line shares a baseline with the example's last line
   (card text baseline sits 30px above the card edge; source baseline ~5.2px above its box) */
.hscroll .page:first-child { padding-bottom: 24.8px; }
.actions { display: flex; gap: 10px; }

.ex { border: 1.5px solid var(--line); border-radius: 28px; padding: 20px 20px 22px; }
.lbl { margin: 0 0 6px; font-size: var(--text-caption); font-weight: 600; color: var(--faint); }
.q { margin: 0; font-size: var(--text-body); line-height: 1.5; text-wrap: pretty; }
.q.dim { font-size: var(--text-ui); color: var(--faint); text-decoration: line-through; text-decoration-thickness: 1px; text-decoration-color: rgba(244,244,242,.35); }
.rule { height: 1.5px; background: var(--line); opacity: .15; margin: 16px 0 14px; border: 0; }

.pager { display: flex; align-items: center; gap: 6px; padding: 12px 28px 0; } /* 12 + the swipe area's 6px = the same 18px gap */ /* same gap below the idea and the examples */
.pager .pdot { position: relative; flex: none; width: 7px; height: 7px; padding: 0; border-radius: 99px; border: 1.5px solid var(--line); background: transparent; cursor: pointer; transition: width .45s var(--spring), background .2s var(--ease); }
.pager .pdot.on { width: 22px; background: var(--ink); }
.pager .pdot::after { content: ""; position: absolute; inset: -18px -3px; } /* 43px tall tap area, no overlap */
.page.ahead { cursor: pointer; }
.slide.end { padding-bottom: 120px; }
.endcard { padding: 0 28px; max-width: 536px; }
.endcard .desc { margin-bottom: 24px; }

/* Shared button language */
.btn {
  height: 44px; padding: 0 20px; border-radius: 999px; border: 1.5px solid var(--line); background: transparent; color: var(--ink);
  font: inherit; font-size: var(--text-ui); font-weight: 600; cursor: pointer;
  transition: border-radius .35s var(--spring), background .2s var(--ease), color .2s var(--ease), transform .35s var(--spring);
}
.btn.solid { background: var(--ink); color: var(--bg); }
.btn.round { width: 44px; padding: 0; font-size: var(--text-body); }
.btn:active { border-radius: 14px; transform: scale(.97); background: var(--ink); color: var(--bg); }

.nav { position: fixed; left: 0; right: 0; bottom: 0; z-index: 10; padding: 0 16px calc(14px + env(safe-area-inset-bottom, 0px)); display: flex; justify-content: center; pointer-events: none; }
.tabs { pointer-events: auto; position: relative; display: flex; width: 100%; max-width: 320px; padding: 4px; border-radius: 999px; border: 1.5px solid rgba(244, 244, 242, .55); background: var(--bg); }
.indicator { position: absolute; top: 4px; bottom: 4px; left: 0; border-radius: 999px; background: var(--ink); transition: transform .5s var(--spring), width .5s var(--spring), border-radius .35s var(--spring); }
.tabs.pressing .indicator { border-radius: 14px; }
.tab { position: relative; z-index: 1; flex: 1; min-width: 0; height: 40px; border: 0; border-radius: 999px; background: transparent; color: var(--muted); font: inherit; font-size: var(--text-caption); font-weight: 600; cursor: pointer; transition: color .25s var(--ease); }
.tab[aria-pressed="true"] { color: var(--bg); }

button:focus-visible { outline: 2px solid var(--ink); outline-offset: 3px; }

/* Quiz */
/* Menu: main group (Discover · Topics · Quiz) or topic group (✕ + scrolling chips) */
.tabs { overflow: hidden; transition: max-width .5s var(--spring); }
.tabs.topicmode { max-width: 440px; }
.mgroup, .tgroup { display: flex; flex: 1 1 auto; min-width: 0; }
.tgroup { display: none; }
.tabs.topicmode .mgroup { display: none; }
.tabs.topicmode .tgroup { display: flex; animation: slidein .4s var(--ease) both; }
.tabs:not(.topicmode) .mgroup { animation: slidein-back .4s var(--ease) both; }
.tabs.topicmode .indicator { opacity: 0; }
@keyframes slidein { from { opacity: 0; transform: translateX(24px); } }
@keyframes slidein-back { from { opacity: 0; } } /* fade only: the Discover indicator is measured against this group */
.tab { flex: 1 1 auto; padding: 0 14px; white-space: nowrap; font-stretch: 94%; }
.tclose { flex: none; width: 40px; height: 40px; border: 0; border-radius: 999px; background: none; color: var(--muted); font: inherit; font-size: var(--text-caption); cursor: pointer; }
.trow { position: relative; display: flex; flex: 1 1 auto; min-width: 0; overflow-x: auto; scrollbar-width: none; scroll-padding: 0 8px; }
.trow::-webkit-scrollbar { display: none; }
/* soft fade on the right edge says "there's more"; the spacer lets the last chip scroll clear of it */
.trow { -webkit-mask-image: linear-gradient(to right, #000 calc(100% - 28px), transparent); mask-image: linear-gradient(to right, #000 calc(100% - 28px), transparent); }
.trow::after { content: ""; flex: 0 0 20px; }
.tind { position: absolute; top: 0; bottom: 0; left: 0; border-radius: 999px; background: var(--ink); opacity: 0; transition: transform .5s var(--spring), width .5s var(--spring), opacity .2s var(--ease); }
.tind.on { opacity: 1; }
.tchip { position: relative; z-index: 1; flex: none; display: inline-flex; align-items: center; height: 40px; padding: 0 14px; border: 0; border-radius: 999px; background: none; color: var(--muted); font: inherit; font-size: var(--text-caption); font-weight: 600; font-stretch: 94%; white-space: nowrap; cursor: pointer; transition: color .25s var(--ease); }
.tchip .dot { width: 8px; height: 8px; margin-right: 7px; vertical-align: 0; }
.tchip[aria-pressed="true"] { color: var(--bg); }
.count { transition: opacity .3s var(--ease); }
.nav { transition: transform .45s var(--ease); }
body.quizzing .feed, body.quizzing .count { opacity: 0; pointer-events: none; }
body.quizzing .nav { transform: translateY(140%); }

/* Intro */
.intro { position: absolute; inset: 0; z-index: 8; display: flex; flex-direction: column; justify-content: flex-end; align-items: center; text-align: center; padding: 0 28px calc(56px + env(safe-area-inset-bottom, 0px)); cursor: pointer; transition: opacity .5s var(--ease); }
.intro[hidden] { display: none; }
.intro.gone { opacity: 0; pointer-events: none; }
.ibody { max-width: 480px; }
.ibody > * { animation: rise .6s var(--ease) both; }
.ibody > :nth-child(2) { animation-delay: .12s; }
.ibody > :nth-child(3) { animation-delay: .24s; }
.ibody > :nth-child(4) { animation-delay: .36s; }
.ititle { margin: 0 0 16px; font-weight: 700; font-size: var(--text-display); line-height: 1; letter-spacing: -0.03em; text-wrap: balance; font-variation-settings: "opsz" 144; }
.ilead { margin: 0 auto 20px; max-width: 32ch; font-size: var(--text-lead); line-height: 1.45; color: var(--muted); text-wrap: pretty; }
.igesture { display: grid; justify-content: center; gap: 6px; margin: 0 0 28px; font-size: var(--text-label); line-height: 1.4; color: var(--faint); }
.igesture span { display: flex; align-items: center; gap: 10px; }
.igesture b { width: 1.25em; font-size: var(--text-body); font-weight: 400; color: var(--muted); text-align: center; }
.intro.brief { cursor: default; }
.intro.brief .ilead, .intro.brief .igesture, .intro.brief .btn { display: none; }
.intro.brief .ititle { margin: 0; }
body.introing .feed, body.introing .count, body.introing .infobtn { opacity: 0; pointer-events: none; }
body.introing .nav { transform: translateY(140%); }
.areplay { margin: 4px 0 0; }
.areplay .linkbtn { padding: 0; min-height: 36px; }
.quiz { position: absolute; inset: 0; z-index: 6; display: flex; flex-direction: column; padding: 64px 28px 28px; overflow-y: auto; scrollbar-width: none; }
.quiz[hidden] { display: none; }
.qtop { position: absolute; left: 28px; right: 20px; top: 10px; display: flex; align-items: center; justify-content: space-between; }
.qtop .btn.round { width: 36px; height: 36px; font-size: var(--text-label); }
.qprog { margin: 0; font-size: var(--text-caption); color: var(--faint); font-variant-numeric: tabular-nums; }
.qprog b { color: var(--ink); font-weight: 600; }
.qbody { margin-top: auto; width: 100%; max-width: 480px; }
.qbody > * { animation: rise .45s var(--ease) both; }
.qbody > :nth-child(2) { animation-delay: .05s; }
.qbody > :nth-child(3) { animation-delay: .1s; }
.qbody > :nth-child(4) { animation-delay: .15s; }
@keyframes rise { from { opacity: 0; transform: translateY(16px); } }
.qtext { margin: 0 0 24px; font-size: var(--text-question); line-height: 1.4; font-weight: 600; letter-spacing: -0.01em; text-wrap: pretty; }
.qtext.dim { color: var(--muted); }
.opts { display: grid; gap: 10px; }
.btn.opt { height: auto; min-height: 52px; padding: 12px 20px; border-radius: 20px; text-align: left; display: flex; align-items: center; justify-content: space-between; gap: 12px; }
.btn.opt:disabled { cursor: default; }
.btn.opt:disabled:active { transform: none; border-radius: 20px; background: transparent; color: var(--ink); }
.btn.opt.right, .btn.opt.right:active { background: var(--ink); color: var(--bg); }
.btn.opt.wrong { opacity: .4; text-decoration: line-through; }
.reveal { margin: 20px 0 20px; }
.reveal h3 { margin: 0 0 6px; font-size: var(--text-body); font-weight: 700; }
.reveal p { margin: 0 0 6px; font-size: var(--text-ui); line-height: 1.5; color: var(--muted); text-wrap: pretty; }
.qactions { display: flex; gap: 10px; flex-wrap: wrap; }
.score { margin: 0 0 12px; font-size: var(--text-score); font-weight: 700; line-height: 1; letter-spacing: -0.04em; font-variation-settings: "opsz" 144; }
.qask { margin: 0 0 10px; font-size: var(--text-ui); line-height: 1.4; font-weight: 600; color: var(--muted); }
.qactions { align-items: center; }
.linkbtn { min-height: 44px; padding: 0 4px; border: 0; background: none; color: var(--muted); font: inherit; font-size: var(--text-label); cursor: pointer; text-decoration: underline; text-decoration-thickness: 1px; text-underline-offset: 3px; text-decoration-color: rgba(244, 244, 242, .35); transition: color .15s var(--ease); }
.linkbtn:hover { color: var(--ink); }
.missed { margin-top: 32px; }
.missed ul { margin: 0; padding: 0; list-style: none; border-top: 1.5px solid rgba(244, 244, 242, .15); }
.missedbtn { display: flex; align-items: center; gap: 0; width: 100%; min-height: 52px; padding: 12px 0; border: 0; border-bottom: 1.5px solid rgba(244, 244, 242, .15); background: none; color: var(--ink); font: inherit; font-size: var(--text-body); text-align: left; cursor: pointer; }
.missedbtn .arrow { margin-left: auto; padding-left: 12px; color: var(--faint); transition: transform .2s var(--ease), color .15s var(--ease); }
.missedbtn:hover .arrow { color: var(--ink); transform: translateX(3px); }

/* About and credits */
/* small visible circle, 44px hit area via ::after */
.btn.infobtn { position: absolute; right: 22px; top: 14px; z-index: 3; width: 26px; height: 26px; padding: 0; border-width: 1.25px; color: var(--muted); border-color: var(--faint); font-size: var(--text-caption); font-style: italic; font-family: Georgia, serif; line-height: 1; transition: opacity .3s var(--ease), border-radius .35s var(--spring), background .2s var(--ease), color .2s var(--ease), transform .35s var(--spring); }
.btn.infobtn::after { content: ""; position: absolute; inset: -9px; }
.btn.infobtn:active { border-radius: 9px; }
body.quizzing .infobtn { opacity: 0; pointer-events: none; }
a.btn { display: inline-flex; align-items: center; text-decoration: none; }
a:focus-visible { outline: 2px solid var(--ink); outline-offset: 3px; }

/* Credits page: a top-aligned colophon, unlike the bottom-anchored sparks and quiz */
.stage { transition: opacity .3s var(--ease); }
body.abouting .stage { opacity: 0; }
.about { position: absolute; inset: 0; z-index: 6; overflow-y: auto; scrollbar-width: none; padding: 76px 28px calc(32px + env(safe-area-inset-bottom, 0px)); }
.about[hidden] { display: none; }
/* header and close stay put while the credits scroll; content fades under it */
.about .qtop { position: fixed; top: 0; left: 0; right: 0; z-index: 1; padding: 10px 20px 14px 28px; background: linear-gradient(var(--bg) 75%, transparent); }
.abody { max-width: 480px; }
.abody > * { animation: rise .45s var(--ease) both; }
.abody > :nth-child(2) { animation-delay: .04s; }
.abody > :nth-child(3) { animation-delay: .08s; }
.abody > :nth-child(4) { animation-delay: .12s; }
.abody > :nth-child(n+5) { animation-delay: .16s; }
.adots { display: flex; gap: 6px; margin: 0 0 18px; }
.adots span { width: 10px; height: 10px; border-radius: 50%; }
.atitle { margin: 0 0 10px; font-weight: 700; font-size: var(--text-title); line-height: 1.06; letter-spacing: -0.025em; text-wrap: balance; font-variation-settings: "opsz" 144; }
.credits { margin: 28px 0 0; border-top: 1.5px solid rgba(244, 244, 242, .15); }
.credits > div { display: grid; grid-template-columns: 92px 1fr; gap: 12px; padding: 14px 0; border-bottom: 1.5px solid rgba(244, 244, 242, .15); }
.credits dt { padding-top: 2px; font-size: var(--text-caption); font-weight: 600; color: var(--faint); }
.credits dd { margin: 0; font-size: var(--text-body); line-height: 1.5; text-wrap: pretty; }
.credits a { color: var(--ink); text-decoration: underline; text-decoration-thickness: 1px; text-underline-offset: 3px; text-decoration-color: rgba(244, 244, 242, .4); transition: text-decoration-color .15s var(--ease); }
.credits a:hover { text-decoration-color: var(--ink); }
.credits .alinks { display: flex; flex-wrap: wrap; gap: 12px 14px; }
.credits .alinks a { padding: 10px 0; margin: -10px 0; } /* taller tap target, same layout */
@media (display-mode: standalone) { .ahome { display: none; } } /* already installed */

@media (prefers-reduced-motion: reduce) {
  .btn, .indicator, .tab, .feed, .pager .pdot, .nav, .count, .btn.infobtn, .intro, .tabs, .tind, .tchip { transition: none; }
  .tgroup, .mgroup { animation: none !important; }
  .ibody > * { animation: none; }
  .qbody > *, .abody > * { animation: none; }
  .stage { transition: none; }
}