/* =========================================================
   PIOT — B&W sleek
   ========================================================= */
:root{
  --bg:#ffffff;
  --ink:#0a0a0a;
  --ink-2:#1a1a1a;
  --mute:#6b6b6b;
  --mute-2:#9a9a9a;
  --line:#e6e6e6;
  --line-2:#d0d0d0;
  --soft:#f5f5f5;
  --soft-2:#fafafa;
  --hi:#000;
  --ok:#0a0a0a;
  --bad:#0a0a0a;
  --shadow:0 1px 0 rgba(0,0,0,.04), 0 20px 60px -20px rgba(0,0,0,.18);
  --radius:18px;
  --radius-sm:12px;
  --ease:cubic-bezier(.2,.7,.15,1);
  --ease-out:cubic-bezier(.16,1,.3,1);
  --t-fast:.18s;
  --t:.32s;
  --t-slow:.6s;
}

@media (prefers-color-scheme: dark){
  :root{
    --bg:#0a0a0a;
    --ink:#fafafa;
    --ink-2:#eaeaea;
    --mute:#9a9a9a;
    --mute-2:#6b6b6b;
    --line:#1f1f1f;
    --line-2:#2a2a2a;
    --soft:#121212;
    --soft-2:#0e0e0e;
    --hi:#fff;
    --shadow:0 1px 0 rgba(255,255,255,.03), 0 30px 80px -20px rgba(0,0,0,.7);
  }
}

*{box-sizing:border-box}
html,body{margin:0;padding:0}
html{scroll-behavior:smooth}
body{
  font-family:'Inter',-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif;
  background:var(--bg);
  color:var(--ink);
  -webkit-font-smoothing:antialiased;
  text-rendering:optimizeLegibility;
  font-feature-settings:"ss01","cv11";
  letter-spacing:-.01em;
  min-height:100vh;
  overflow-x:hidden;
}
.mono{font-family:'JetBrains Mono',ui-monospace,monospace;letter-spacing:0}

/* film grain */
.grain{
  position:fixed; inset:0; pointer-events:none; z-index:1;
  opacity:.035; mix-blend-mode:multiply;
  background-image:url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='200' height='200'><filter id='n'><feTurbulence type='fractalNoise' baseFrequency='.9' numOctaves='2' stitchTiles='stitch'/></filter><rect width='100%25' height='100%25' filter='url(%23n)'/></svg>");
}
@media (prefers-color-scheme: dark){ .grain{ opacity:.06; mix-blend-mode:screen } }

/* =========================================================
   Top bar
   ========================================================= */
.topbar{
  position:sticky; top:0; z-index:50;
  display:grid; grid-template-columns:1fr auto 1fr;
  align-items:center;
  padding:18px 32px;
  background:color-mix(in srgb, var(--bg) 80%, transparent);
  backdrop-filter:saturate(1.4) blur(14px);
  -webkit-backdrop-filter:saturate(1.4) blur(14px);
  border-bottom:1px solid var(--line);
}
.brand{ display:flex; align-items:center; gap:10px; font-weight:700; letter-spacing:.02em }
.brand-dot{
  width:10px; height:10px; border-radius:50%; background:var(--ink);
  box-shadow:0 0 0 4px color-mix(in srgb, var(--ink) 8%, transparent);
  animation:pulse 2.4s var(--ease) infinite;
}
@keyframes pulse{
  0%,100%{ box-shadow:0 0 0 0 color-mix(in srgb, var(--ink) 22%, transparent) }
  50%   { box-shadow:0 0 0 8px color-mix(in srgb, var(--ink) 0%, transparent) }
}
.brand-name{ font-size:15px }
.brand-sub{ color:var(--mute); font-weight:500; font-size:13px }

.tabs{
  position:relative;
  display:flex; gap:4px;
  background:var(--soft);
  padding:5px;
  border-radius:999px;
  border:1px solid var(--line);
}
.tab{
  position:relative; z-index:1;
  display:flex; align-items:center; gap:8px;
  padding:9px 18px;
  border:0; background:transparent;
  color:var(--mute);
  font:600 13px/1 'Inter',sans-serif;
  letter-spacing:.02em;
  border-radius:999px;
  cursor:pointer;
  transition:color var(--t) var(--ease);
}
.tab:hover{ color:var(--ink) }
.tab.active{ color:var(--bg) }
.tab-num{
  font-family:'JetBrains Mono',monospace;
  font-size:10px; opacity:.6;
}
.tab-indicator{
  position:absolute; top:5px; left:5px;
  height:calc(100% - 10px);
  background:var(--ink);
  border-radius:999px;
  transition:transform var(--t) var(--ease-out), width var(--t) var(--ease-out);
  z-index:0;
}

.meta{ display:flex; justify-content:flex-end; color:var(--mute); font:500 12px/1 'JetBrains Mono',monospace }

/* =========================================================
   Stage / panels
   ========================================================= */
.stage{
  position:relative; z-index:2;
  max-width:980px; margin:0 auto;
  padding:64px 32px 120px;
  min-height:calc(100vh - 120px);
}
.panel{
  display:none;
  animation:panelIn .55s var(--ease-out) both;
}
.panel.active{ display:block }
@keyframes panelIn{
  from{ opacity:0; transform:translateY(8px) }
  to  { opacity:1; transform:none }
}

.screen{ display:none }
.screen.show{ display:block; animation:screenIn .5s var(--ease-out) both }
@keyframes screenIn{
  from{ opacity:0; transform:translateY(12px) }
  to  { opacity:1; transform:none }
}

/* =========================================================
   Hero / intro
   ========================================================= */
.hero{ padding:24px 0 0 }
.hero-eyebrow{
  display:inline-block;
  font:600 11px/1 'JetBrains Mono',monospace;
  letter-spacing:.18em; text-transform:uppercase;
  color:var(--mute);
  padding:8px 12px;
  border:1px solid var(--line);
  border-radius:999px;
  margin-bottom:24px;
  animation:revealUp .7s var(--ease-out) both;
}
.hero-title{
  font-size:clamp(48px, 8vw, 96px);
  line-height:.95;
  letter-spacing:-.04em;
  font-weight:800;
  margin:0 0 28px;
}
.hero-line{
  display:block;
  overflow:hidden;
}
.hero-line > *, .hero-line{ animation:revealUp .9s var(--ease-out) both }
.hero-line:nth-child(1){ animation-delay:.05s }
.hero-line:nth-child(2){ animation-delay:.15s }
.hero-line:nth-child(3){ animation-delay:.25s }
.hero-line em{
  font-style:normal;
  background:linear-gradient(90deg, var(--ink) 0%, var(--mute) 100%);
  -webkit-background-clip:text; background-clip:text;
  color:transparent;
  font-weight:800;
}
@keyframes revealUp{
  from{ opacity:0; transform:translateY(30px) }
  to  { opacity:1; transform:none }
}

.hero-lead{
  max-width:520px;
  color:var(--mute);
  font-size:17px; line-height:1.55;
  margin:0 0 40px;
  animation:revealUp .9s .35s var(--ease-out) both;
}

.controls{
  display:flex; gap:32px; flex-wrap:wrap;
  margin-bottom:36px;
  animation:revealUp .9s .45s var(--ease-out) both;
}
.ctrl label{
  display:block;
  font:600 11px/1 'JetBrains Mono',monospace;
  letter-spacing:.16em; text-transform:uppercase;
  color:var(--mute);
  margin-bottom:10px;
}
.ctrl .hint{ margin-top:8px; font-size:12px; color:var(--mute-2) }

.seg{
  display:inline-flex; gap:0;
  border:1px solid var(--line);
  border-radius:12px;
  padding:4px;
  background:var(--soft);
}
.seg button{
  padding:8px 14px;
  border:0; background:transparent;
  color:var(--mute);
  font:600 13px/1 'Inter',sans-serif;
  border-radius:8px;
  cursor:pointer;
  transition:all var(--t) var(--ease);
}
.seg button:hover{ color:var(--ink) }
.seg button.active{
  background:var(--ink); color:var(--bg);
  box-shadow:0 4px 14px -4px color-mix(in srgb, var(--ink) 50%, transparent);
}

/* CTA */
.cta{
  display:inline-flex; align-items:center; gap:10px;
  padding:16px 26px;
  background:var(--ink); color:var(--bg);
  border:0; border-radius:999px;
  font:600 14px/1 'Inter',sans-serif;
  letter-spacing:.02em;
  cursor:pointer;
  position:relative; overflow:hidden;
  transition:transform var(--t) var(--ease), box-shadow var(--t) var(--ease);
  box-shadow:0 8px 22px -8px color-mix(in srgb, var(--ink) 55%, transparent);
  animation:revealUp .9s .55s var(--ease-out) both;
}
.cta.small{ padding:12px 18px; font-size:13px; animation:none }
.cta:hover{ transform:translateY(-2px); box-shadow:0 14px 28px -10px color-mix(in srgb, var(--ink) 65%, transparent) }
.cta:active{ transform:translateY(0) }
.cta svg{ transition:transform var(--t) var(--ease) }
.cta:hover svg{ transform:translateX(3px) }
.cta::after{
  content:""; position:absolute; inset:0;
  background:radial-gradient(180px 60px at var(--mx,50%) var(--my,50%), color-mix(in srgb, var(--bg) 18%, transparent), transparent 60%);
  opacity:0; transition:opacity var(--t) var(--ease);
  pointer-events:none;
}
.cta:hover::after{ opacity:1 }

.ghost{
  background:transparent; color:var(--ink);
  border:1px solid var(--line);
  padding:12px 18px; border-radius:999px;
  font:600 13px/1 'Inter',sans-serif;
  cursor:pointer;
  transition:all var(--t) var(--ease);
}
.ghost:hover{ border-color:var(--ink); background:var(--soft) }

.kbd-row{
  display:flex; gap:24px; flex-wrap:wrap;
  margin-top:36px;
  color:var(--mute);
  font-size:12px;
  animation:revealUp .9s .7s var(--ease-out) both;
}
kbd{
  display:inline-block;
  font:600 11px/1 'JetBrains Mono',monospace;
  padding:3px 6px; margin-right:4px;
  background:var(--soft); border:1px solid var(--line);
  border-bottom-width:2px;
  border-radius:5px;
  color:var(--ink);
}

/* =========================================================
   Quiz
   ========================================================= */
.quiz-head{
  display:flex; align-items:center; gap:18px;
  margin-bottom:28px;
}
.qcount{
  font:600 13px/1 'JetBrains Mono',monospace;
  color:var(--ink);
}
.qcount .slash, .qcount #qTotal{ color:var(--mute) }
.progress{
  flex:1; height:2px;
  background:var(--line);
  border-radius:2px; overflow:hidden;
}
.progress-fill{
  height:100%; width:0;
  background:var(--ink);
  transition:width var(--t-slow) var(--ease-out);
}

.qcard{
  padding:8px 0;
  animation:qIn .45s var(--ease-out) both;
}
.qcard.out{ animation:qOut .25s var(--ease) both }
@keyframes qIn{
  from{ opacity:0; transform:translateY(14px) }
  to  { opacity:1; transform:none }
}
@keyframes qOut{
  to{ opacity:0; transform:translateY(-10px) }
}

.qtopic{
  display:inline-block;
  font:600 11px/1 'JetBrains Mono',monospace;
  letter-spacing:.16em; text-transform:uppercase;
  color:var(--mute);
  padding:6px 10px;
  border:1px solid var(--line);
  border-radius:999px;
  margin-bottom:18px;
}
.qtext{
  font-size:clamp(24px, 3.4vw, 34px);
  line-height:1.25; letter-spacing:-.02em;
  font-weight:600;
  margin:0 0 32px;
  max-width:780px;
}
.answers{
  display:grid; gap:12px;
}
.ans{
  position:relative;
  display:grid; grid-template-columns:auto 1fr auto; align-items:center; gap:16px;
  padding:18px 22px;
  background:var(--bg);
  border:1px solid var(--line);
  border-radius:var(--radius);
  cursor:pointer;
  text-align:left;
  font:500 16px/1.4 'Inter',sans-serif;
  color:var(--ink);
  transition:transform var(--t) var(--ease), border-color var(--t) var(--ease), background var(--t) var(--ease), box-shadow var(--t) var(--ease);
  animation:ansIn .5s var(--ease-out) both;
}
.ans:nth-child(1){ animation-delay:.05s }
.ans:nth-child(2){ animation-delay:.10s }
.ans:nth-child(3){ animation-delay:.15s }
.ans:nth-child(4){ animation-delay:.20s }
@keyframes ansIn{
  from{ opacity:0; transform:translateY(10px) }
  to  { opacity:1; transform:none }
}
.ans:hover{
  border-color:var(--ink);
  transform:translateY(-1px);
  box-shadow:var(--shadow);
}
.ans-letter{
  width:32px; height:32px;
  display:grid; place-items:center;
  border:1px solid var(--line);
  border-radius:8px;
  font:700 13px/1 'JetBrains Mono',monospace;
  background:var(--soft);
  transition:all var(--t) var(--ease);
}
.ans:hover .ans-letter{
  background:var(--ink); color:var(--bg); border-color:var(--ink);
}
.ans-text{ flex:1 }
.ans-mark{
  width:22px; height:22px;
  opacity:0; transform:scale(.6);
  transition:all var(--t) var(--ease);
}
.ans.correct{
  border-color:var(--ink); background:var(--ink); color:var(--bg);
}
.ans.correct .ans-letter{ background:var(--bg); color:var(--ink); border-color:var(--bg) }
.ans.correct .ans-mark{ opacity:1; transform:scale(1) }
.ans.wrong{
  border-color:var(--ink-2);
  background:var(--soft);
  color:var(--mute);
  text-decoration:line-through;
}
.ans.wrong .ans-letter{ background:var(--bg); color:var(--mute) }
.ans.disabled{ pointer-events:none }
.ans.shake{ animation:shake .45s var(--ease) }
@keyframes shake{
  0%,100%{ transform:translateX(0) }
  20%{ transform:translateX(-6px) }
  40%{ transform:translateX(5px) }
  60%{ transform:translateX(-3px) }
  80%{ transform:translateX(2px) }
}

.qfoot{
  margin-top:24px;
  display:flex; align-items:flex-start; justify-content:space-between; gap:24px;
  min-height:40px;
}
.explain{
  font-size:14px; line-height:1.5;
  color:var(--mute);
  max-width:640px;
  opacity:0; transform:translateY(6px);
  transition:opacity var(--t) var(--ease), transform var(--t) var(--ease);
}
.explain.show{ opacity:1; transform:none }
.explain b{ color:var(--ink); font-weight:600 }
.hidden{ display:none !important }

/* =========================================================
   Results
   ========================================================= */
.res{ padding:24px 0; max-width:760px; margin:0 auto; text-align:center }
.res-eyebrow{
  font:600 11px/1 'JetBrains Mono',monospace;
  letter-spacing:.18em; text-transform:uppercase;
  color:var(--mute);
  margin-bottom:16px;
}
.res-score{
  font-weight:800;
  font-size:clamp(96px, 18vw, 200px);
  line-height:.9;
  letter-spacing:-.05em;
  margin:0 0 12px;
  display:inline-flex; align-items:baseline;
}
.res-score .pct{ font-size:.35em; color:var(--mute); margin-left:6px }
#scorePct{ background:linear-gradient(180deg, var(--ink) 0%, var(--mute) 130%); -webkit-background-clip:text; background-clip:text; color:transparent }
.res-line{ color:var(--mute); font-size:15px; margin-bottom:28px }
.res-bar{
  height:6px; background:var(--soft); border-radius:6px; overflow:hidden;
  border:1px solid var(--line);
  margin:0 auto 36px; max-width:520px;
}
#resBar{ height:100%; width:0; background:var(--ink); transition:width 1.2s var(--ease-out) }
.res-grid{
  display:grid; grid-template-columns:repeat(auto-fit,minmax(150px,1fr));
  gap:14px;
  margin-bottom:36px;
  text-align:left;
}
.res-cell{
  padding:18px 16px;
  border:1px solid var(--line);
  border-radius:var(--radius-sm);
  background:var(--soft-2);
}
.res-cell .k{ font:600 10px/1 'JetBrains Mono',monospace; letter-spacing:.18em; text-transform:uppercase; color:var(--mute); margin-bottom:8px }
.res-cell .v{ font-size:24px; font-weight:700; letter-spacing:-.02em }
.res-actions{ display:flex; justify-content:center; gap:12px; flex-wrap:wrap }

/* =========================================================
   Materials
   ========================================================= */
.mat-head{
  display:flex; align-items:end; justify-content:space-between; gap:24px; flex-wrap:wrap;
  margin-bottom:36px;
  padding-top:24px;
}
.mat-head h2{
  font-size:clamp(40px, 6vw, 64px);
  line-height:.95; letter-spacing:-.03em;
  font-weight:800; margin:0;
}
.search{
  flex:1; min-width:260px;
  padding:14px 18px;
  border:1px solid var(--line);
  border-radius:999px;
  background:var(--soft);
  color:var(--ink);
  font:500 14px/1 'Inter',sans-serif;
  outline:none;
  transition:all var(--t) var(--ease);
}
.search:focus{ border-color:var(--ink); background:var(--bg); box-shadow:0 0 0 4px color-mix(in srgb, var(--ink) 8%, transparent) }
.search::placeholder{ color:var(--mute-2) }

.mat-list{ display:grid; gap:10px }

.mat{
  border:1px solid var(--line);
  border-radius:var(--radius);
  background:var(--bg);
  overflow:hidden;
  transition:border-color var(--t) var(--ease), box-shadow var(--t) var(--ease);
}
.mat:hover{ border-color:var(--line-2) }
.mat.open{ border-color:var(--ink); box-shadow:var(--shadow) }

.mat-summary{
  display:grid; grid-template-columns:auto 1fr auto auto; align-items:center; gap:16px;
  padding:20px 24px;
  cursor:pointer;
  list-style:none;
  user-select:none;
}
.mat-summary::-webkit-details-marker{ display:none }
.mat-num{
  font:700 11px/1 'JetBrains Mono',monospace;
  letter-spacing:.1em;
  color:var(--mute);
  width:28px;
}
.mat-title{ font-weight:600; font-size:17px; letter-spacing:-.01em }
.mat-tag{
  font:600 10px/1 'JetBrains Mono',monospace;
  letter-spacing:.14em; text-transform:uppercase;
  color:var(--mute);
  padding:5px 10px;
  border:1px solid var(--line);
  border-radius:999px;
}
.mat-caret{
  width:24px; height:24px;
  display:grid; place-items:center;
  border:1px solid var(--line);
  border-radius:50%;
  transition:transform var(--t) var(--ease), background var(--t) var(--ease), color var(--t) var(--ease);
  color:var(--mute);
}
.mat.open .mat-caret{ transform:rotate(45deg); background:var(--ink); color:var(--bg); border-color:var(--ink) }
.mat-caret svg{ width:12px; height:12px }

.mat-body{
  display:grid; grid-template-rows:0fr;
  transition:grid-template-rows var(--t-slow) var(--ease-out);
}
.mat-body > div{ overflow:hidden; min-height:0 }
.mat.open .mat-body{ grid-template-rows:1fr }
.mat-content{
  padding:0 24px 24px;
  color:var(--ink-2);
  font-size:15px; line-height:1.65;
}
.mat-content h4{
  font:600 11px/1 'JetBrains Mono',monospace;
  letter-spacing:.16em; text-transform:uppercase;
  color:var(--mute);
  margin:18px 0 8px;
}
.mat-content ul{ margin:0 0 8px; padding-left:18px }
.mat-content li{ margin-bottom:4px }
.mat-content code{
  font-family:'JetBrains Mono',monospace; font-size:13px;
  background:var(--soft); padding:1px 6px; border-radius:4px;
}
.mat-content p{ margin:0 0 10px }
.mat-content table{
  width:100%; border-collapse:collapse; margin:8px 0;
  font-size:13px;
}
.mat-content th, .mat-content td{
  text-align:left; padding:8px 10px;
  border-bottom:1px solid var(--line);
}
.mat-content th{ font:600 11px/1 'JetBrains Mono',monospace; letter-spacing:.12em; text-transform:uppercase; color:var(--mute) }
.mat-content .row{ display:flex; gap:8px; flex-wrap:wrap; margin:6px 0 14px }
.mat-content .chip{
  display:inline-block;
  padding:5px 10px;
  background:var(--soft); border:1px solid var(--line);
  border-radius:999px;
  font:600 11px/1 'JetBrains Mono',monospace;
  color:var(--ink);
}

/* search hide */
.mat.hide{ display:none }

/* =========================================================
   Footer
   ========================================================= */
.footbar{
  position:fixed; left:0; right:0; bottom:0;
  display:flex; justify-content:space-between;
  padding:14px 32px;
  font-size:11px; color:var(--mute);
  border-top:1px solid var(--line);
  background:color-mix(in srgb, var(--bg) 80%, transparent);
  backdrop-filter:blur(10px);
  -webkit-backdrop-filter:blur(10px);
  z-index:40;
}

/* =========================================================
   Mobile
   ========================================================= */
@media (max-width:720px){
  .topbar{ grid-template-columns:auto 1fr; padding:14px 18px }
  .topbar .meta{ display:none }
  .stage{ padding:36px 18px 100px }
  .controls{ gap:20px }
  .hero-title{ font-size:14vw }
  .tabs{ justify-self:end }
  .tab{ padding:8px 14px }
  .tab-label{ font-size:12px }
  .footbar{ padding:10px 18px; font-size:10px }
  .ans{ padding:14px 16px; gap:12px }
  .qtext{ font-size:22px }
}

/* reduce motion */
@media (prefers-reduced-motion: reduce){
  *,*::before,*::after{ animation-duration:.01ms !important; transition-duration:.01ms !important }
}