:root{
  --paper:#f4efe6; --card:#fffaf1; --ink:#1c1a2b; --muted:#615c74;
  --blue:#2c4bd8; --pink:#ff3e9a; --yellow:#ffc53d; --teal:#1fa88a;
  --line:rgba(28,26,43,.16);
  --serif:"Source Serif 4",Georgia,serif;
  --display:"Fraunces",Georgia,serif;
  --mono:"JetBrains Mono",ui-monospace,Menlo,monospace;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth;-webkit-text-size-adjust:100%}
body{
  margin:0;background:var(--paper);color:var(--ink);
  font-family:var(--serif);font-size:clamp(17px,.55vw + 14.5px,20px);line-height:1.62;
  -webkit-font-smoothing:antialiased;overflow-x:hidden;
}
/* paper grain */
body::after{
  content:"";position:fixed;inset:0;pointer-events:none;z-index:40;opacity:.22;
  background-image:url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='180' height='180'><filter id='n'><feTurbulence type='fractalNoise' baseFrequency='.85' numOctaves='2' stitchTiles='stitch'/><feColorMatrix values='0 0 0 0 .11 0 0 0 0 .1 0 0 0 0 .17 0 0 0 .55 0'/></filter><rect width='100%' height='100%' filter='url(%23n)'/></svg>");
}
.sr-only{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}
#progress{position:fixed;top:0;left:0;height:4px;width:0;background:var(--pink);z-index:60}

.wrap{max-width:680px;margin:0 auto;padding:0 20px}
a{color:var(--blue);text-decoration-thickness:2px;text-underline-offset:3px}
strong{font-weight:700}
sup{font-size:.62em;line-height:0}
code{font-family:var(--mono);font-size:.86em;background:rgba(255,62,154,.12);padding:1px 6px;border-radius:5px}

/* hero */
.hero{padding:28px 0 10px}
.kicker{font-family:var(--mono);font-size:12px;letter-spacing:.14em;text-transform:uppercase;color:var(--pink);text-align:center;margin:0 0 6px}
.hero-stage{max-width:1180px;margin:0 auto;padding:0 12px}
#hero-canvas{display:block;width:100%;touch-action:pan-y}
.hero-controls{
  max-width:860px;margin:6px auto 0;padding:0 20px;
  display:flex;flex-wrap:wrap;gap:10px 14px;align-items:center;justify-content:center;
}
.scrub,.hero-meter{display:flex;align-items:center;gap:8px;font-family:var(--mono);font-size:12px;text-transform:uppercase;letter-spacing:.08em;color:var(--muted)}
.scrub{flex:1 1 220px}
.scrub input{flex:1}
.hero-meter .meter{width:120px}
.lede{font-family:var(--display);font-weight:500;font-size:clamp(23px,2.4vw + 12px,34px);line-height:1.2;letter-spacing:-.01em;text-align:center;margin:26px 0 14px;font-variation-settings:"opsz" 72}
.caption{color:var(--muted);text-align:center;font-size:.92em;margin:0 auto;max-width:600px;min-height:4.8em;transition:color .3s}
.caption.flash{color:var(--ink)}
.toc{display:flex;flex-wrap:wrap;justify-content:center;gap:8px;margin:22px 0 0}
.toc a{font-family:var(--mono);font-size:13px;color:var(--ink);text-decoration:none;border:2px solid var(--ink);border-radius:999px;padding:5px 12px 5px 6px;background:var(--card);transition:background .15s}
.toc a b{display:inline-grid;place-items:center;width:20px;height:20px;border-radius:50%;background:var(--pink);color:#fff;font-size:11px;margin-right:6px}
.toc a:hover{background:var(--yellow)}

/* chapters */
.chapter{padding:64px 0 10px}
h2{
  font-family:var(--display);font-weight:800;font-size:clamp(36px,4.6vw + 14px,62px);
  line-height:1;letter-spacing:-.025em;margin:0 0 22px;font-variation-settings:"opsz" 144;
}
h2 .num{
  display:block;font-size:max(.5em,26px);letter-spacing:.04em;margin-bottom:6px;
  color:transparent;-webkit-text-stroke:1.5px var(--pink);
}
h2.small-h{font-size:clamp(28px,2.6vw + 14px,40px);margin-top:36px}
h3{font-family:var(--display);font-weight:700;font-size:23px;line-height:1.15;margin:0 0 6px}
p{margin:0 0 1em}

/* demo cards */
.demo{
  max-width:900px;margin:30px auto 34px;padding:18px;
  background:var(--card);border:2px solid var(--ink);border-radius:16px;
  box-shadow:6px 6px 0 var(--pink);
  position:relative;z-index:1;
}
@media (max-width:940px){.demo{margin-left:14px;margin-right:14px}}
@media (max-width:520px){.demo{padding:14px 12px;box-shadow:4px 4px 0 var(--pink)}}
.demo-title{font-family:var(--mono);font-size:12px;letter-spacing:.12em;text-transform:uppercase;color:var(--muted);margin:0 0 12px}
.demo canvas{display:block;width:100%}
.readout{font-family:var(--mono);font-size:13px;line-height:1.5;color:var(--muted);margin:12px 0 0}
.readout b{color:var(--ink)}
.controls{display:flex;flex-wrap:wrap;gap:8px;margin-top:14px;align-items:center}
.controls.center{justify-content:center}

button{
  font-family:var(--mono);font-size:14px;line-height:1.2;padding:9px 14px;
  border:2px solid var(--ink);background:var(--paper);color:var(--ink);border-radius:999px;
  cursor:pointer;transition:transform .08s,background .15s,color .15s;touch-action:manipulation;
  -webkit-tap-highlight-color:transparent;
}
button:hover{background:var(--yellow)}
button:active{transform:translate(1px,1px)}
button:focus-visible,input:focus-visible,a:focus-visible{outline:3px solid var(--blue);outline-offset:2px}
button.primary{background:var(--ink);color:var(--paper)}
button.primary:hover{background:var(--blue)}
button.toggle.on{background:var(--teal);color:#fff;border-color:var(--ink)}
.seg{display:inline-flex;border:2px solid var(--ink);border-radius:999px;overflow:hidden}
.seg button{border:0;border-radius:0;border-right:2px solid var(--ink);padding:9px 14px}
.seg button:last-child{border-right:0}
.seg button.on{background:var(--ink);color:var(--paper)}

input[type=range]{accent-color:var(--pink);width:100%;height:28px;margin:0}
.slider-row{display:flex;align-items:center;gap:14px;margin-top:12px;font-family:var(--mono);font-size:13px;color:var(--muted)}
.slider-row span{white-space:nowrap;min-width:9.5em;flex:none}
.slider-row b{color:var(--ink)}

.meter{height:12px;border:2px solid var(--ink);border-radius:999px;overflow:hidden;background:var(--paper);flex:1}
.meter>i{display:block;height:100%;width:0;background:repeating-linear-gradient(45deg,var(--pink) 0 6px,#ff73b6 6px 12px);transition:width .18s linear}

.stats{display:grid;grid-template-columns:repeat(auto-fit,minmax(150px,1fr));gap:12px 16px;margin-top:14px}
.stat{border-top:2px solid var(--ink);padding-top:6px}
.stat .k{font-family:var(--mono);font-size:11px;text-transform:uppercase;letter-spacing:.08em;color:var(--muted)}
.stat .v{font-family:var(--display);font-weight:700;font-size:22px;line-height:1.25;font-variant-numeric:tabular-nums}
@media (max-width:520px){
  .stats{grid-template-columns:1fr 1fr;gap:10px 14px}
  .stats>.stat:last-child:nth-child(odd){grid-column:1/-1}
  .stat .v{font-size:20px}
}

.callout{margin:28px 0;padding:16px 20px;border-left:6px solid var(--blue);background:rgba(44,75,216,.07);border-radius:0 14px 14px 0}
.callout.pinkline{border-left-color:var(--pink);background:rgba(255,62,154,.07)}
.callout p:last-child{margin-bottom:0}
.callout-k{font-family:var(--mono);font-size:12px;letter-spacing:.12em;text-transform:uppercase;color:var(--muted);margin-bottom:6px}
.formula{font-family:var(--display);font-style:italic;font-weight:600;font-size:40px;line-height:1.1;margin:4px 0 10px;color:var(--blue)}

/* coins */
.coin-cols{display:grid;grid-template-columns:repeat(5,1fr);gap:8px;align-items:end}
.ccol{display:flex;flex-direction:column;align-items:center;gap:4px;min-width:0}
.ccol h4{margin:0 0 2px;font-family:var(--mono);font-size:12px;font-weight:600;text-align:center;white-space:nowrap}
.crow{display:flex;gap:2px;padding:3px;border-radius:7px;transition:background .2s}
.crow.hit{background:var(--yellow);animation:pop .5s}
@keyframes pop{0%{transform:scale(1.25)}100%{transform:scale(1)}}
.coin{width:clamp(11px,2.6vw,20px);height:clamp(11px,2.6vw,20px);border-radius:50%;display:grid;place-items:center;font-family:var(--mono);font-size:clamp(7px,1.4vw,11px);font-weight:600;color:#fff}
.coin.h{background:var(--pink)}
.coin.t{background:var(--blue)}
.cways{font-family:var(--mono);font-size:11px;color:var(--muted);text-align:center;white-space:nowrap}
.ctally{width:100%;height:70px;display:flex;align-items:flex-end;justify-content:center;border-bottom:2px solid var(--ink);margin-top:4px}
.ctally i{display:block;width:62%;background:var(--ink);border-radius:5px 5px 0 0;height:0;transition:height .25s}
.cpct{font-family:var(--mono);font-size:12px;font-weight:600;text-align:center;min-height:1.4em}

/* gas */
.gas-bar{display:flex;align-items:center;gap:12px;margin-top:10px;font-family:var(--mono);font-size:13px}
.gas-bar .lr{white-space:nowrap;display:flex;align-items:center;gap:6px}
.gas-bar .lr b{display:inline-block;min-width:2.2em;font-variant-numeric:tabular-nums}
.gas-bar .meter-wrap{flex:1;display:flex;align-items:center;gap:8px}
.gas-bar .meter-wrap .k{font-size:11px;text-transform:uppercase;letter-spacing:.08em;color:var(--muted)}
.gas-bar .meter-wrap b{min-width:3em;text-align:right;font-variant-numeric:tabular-nums}
.dot{width:10px;height:10px;border-radius:50%;display:inline-block}
.dot.blue{background:var(--blue)} .dot.pink{background:var(--pink)}
.spark{margin-top:8px;height:56px}
.demon-panel{margin-top:12px;padding:12px;border:2px dashed var(--pink);border-radius:12px}
.demon-panel .readout{margin-top:8px}
.hold{width:100%;padding:16px;font-size:16px;background:var(--pink);color:#fff;border-color:var(--ink);user-select:none;-webkit-user-select:none;-webkit-touch-callout:none;touch-action:none}
.hold:hover{background:var(--pink)}
.hold.down{background:var(--ink)}
@media (max-width:520px){
  .gas-bar{flex-wrap:wrap}
  .gas-bar .meter-wrap{order:3;flex-basis:100%}
}

/* quiz */
.clips{display:grid;grid-template-columns:repeat(3,1fr);gap:14px}
@media (max-width:680px){.clips{grid-template-columns:1fr}}
.clip{border:2px solid var(--ink);border-radius:12px;padding:10px;background:var(--paper);display:flex;flex-direction:column}
.clip h4{margin:0 0 6px;font-family:var(--mono);font-size:12px;letter-spacing:.08em;text-transform:uppercase}
.clip canvas{border-radius:8px;background:#fff;align-self:center}
@media (max-width:680px){.clip{display:grid;grid-template-columns:150px 1fr;gap:10px;align-items:start}.clip h4{grid-column:1/-1;margin:0}.clip canvas{width:150px}}
.clip .btns{display:flex;gap:6px;margin-top:8px;flex-wrap:wrap}
@media (max-width:680px){
  .clip .side{display:contents}
  .clip canvas{align-self:start}
  .clip .btns{grid-column:2;margin-top:0;flex-direction:column;align-self:center}
  .clip .res{grid-column:1/-1;margin:0;min-height:0}
  .clip .res:empty{display:none}
}
.clip .btns button{flex:1;padding:8px 6px;font-size:13px}
.clip .res{font-family:var(--mono);font-size:12.5px;line-height:1.45;margin:8px 0 0;min-height:3em;color:var(--muted)}
.clip .res b{color:var(--ink)}
.clip.right{box-shadow:inset 0 0 0 3px var(--teal)}
.clip.wrong{box-shadow:inset 0 0 0 3px var(--pink)}
.clip.trick{box-shadow:inset 0 0 0 3px var(--yellow)}
.clip.done .btns button{opacity:.45;pointer-events:none}

/* shannon */
.presets{display:flex;flex-wrap:wrap;gap:8px;margin-bottom:12px}
.presets button{font-size:13px;padding:7px 12px}
.sh-rows{display:grid;gap:8px}
.sh-row{display:grid;grid-template-columns:7.2em 1fr 3.4em 5.6em;gap:10px;align-items:center;font-family:var(--mono);font-size:13px;padding:4px 6px;border-radius:8px;transition:background .3s}
.sh-row.hit{background:var(--yellow)}
.sh-row .lab{white-space:nowrap}
.sh-row .pc{text-align:right;font-weight:600;font-variant-numeric:tabular-nums}
.sh-row .sur{color:var(--muted);text-align:right;font-variant-numeric:tabular-nums}
@media (max-width:520px){.sh-row{grid-template-columns:6.4em 1fr 3em;}.sh-row .sur{grid-column:2/-1;text-align:left;margin-top:-6px;font-size:11.5px}}
.sh-out{display:grid;grid-template-columns:minmax(220px,1fr) 1.3fr;gap:18px;align-items:center;margin-top:16px;padding-top:14px;border-top:2px solid var(--ink)}
@media (max-width:620px){.sh-out{grid-template-columns:1fr}}
.sh-out .k{font-family:var(--mono);font-size:11px;letter-spacing:.08em;text-transform:uppercase;color:var(--muted)}
.sh-out .big{font-family:var(--display);font-weight:800;font-size:46px;line-height:1.05;font-variant-numeric:tabular-nums}
.sh-out .big small{font-size:.45em;font-weight:600}
.sh-out .meter{margin-top:6px}
.sh-out .scale{display:flex;justify-content:space-between;font-family:var(--mono);font-size:10.5px;color:var(--muted);margin-top:4px}
.sh-out .readout{margin:0}

/* lessons */
.lessons{max-width:960px;margin:10px auto 0;padding:0 20px;display:grid;grid-template-columns:repeat(2,1fr);gap:16px}
@media (max-width:700px){.lessons{grid-template-columns:1fr}}
.lessons article{position:relative;padding:18px 18px 16px 64px;border:2px solid var(--ink);border-radius:14px;background:var(--card)}
.lessons article:nth-child(odd){box-shadow:5px 5px 0 var(--blue)}
.lessons article:nth-child(even){box-shadow:5px 5px 0 var(--yellow)}
.lessons .ln{position:absolute;left:16px;top:12px;font-family:var(--display);font-weight:900;font-size:40px;line-height:1;color:transparent;-webkit-text-stroke:2px var(--pink)}
.lessons p{margin:0;font-size:.95em}

/* big picture */
.sun-svg{width:100%;height:auto;display:block}
.svg-lab{font-family:var(--mono);font-size:14px;fill:var(--ink)}
@media (max-width:520px){.svg-lab{font-size:24px}}
.photon-in{fill:none;stroke:var(--pink);stroke-width:6;stroke-linecap:round;stroke-dasharray:14 10;animation:flow 1.2s linear infinite}
.ir{fill:none;stroke:#e0572e;stroke-width:2.2;stroke-linecap:round;stroke-dasharray:5 5;animation:flow .9s linear infinite}
@keyframes flow{to{stroke-dashoffset:-48}}
.pull{font-family:var(--display);font-weight:700;font-style:italic;font-size:clamp(26px,2.2vw + 14px,36px);line-height:1.2;margin:30px 0 0;padding:4px 0 4px 18px;border-left:6px solid var(--pink)}

/* myths and cheat sheet */
.myth{display:grid;grid-template-columns:1fr;gap:4px;padding:14px 0;border-top:2px solid var(--line)}
.myth .m{font-family:var(--display);font-weight:700;font-size:21px;margin:0;text-decoration:line-through;text-decoration-color:var(--pink);text-decoration-thickness:3px}
.myth .a{margin:0}
.cheat{counter-reset:c;list-style:none;padding:0;margin:0}
.cheat li{counter-increment:c;position:relative;padding:12px 0 12px 46px;border-top:2px solid var(--line)}
.cheat li::before{content:counter(c);position:absolute;left:0;top:10px;width:30px;height:30px;border-radius:50%;background:var(--blue);color:#fff;display:grid;place-items:center;font-family:var(--mono);font-size:13px;font-weight:600}
.deeper{list-style:none;padding:0;margin:0}
.deeper li{padding:10px 0;border-top:2px solid var(--line)}
.deeper li span{display:block;font-size:.85em;color:var(--muted)}
.foot{padding:40px 20px 60px;font-family:var(--mono);font-size:12px;color:var(--muted);text-align:center}

@media (prefers-reduced-motion:reduce){
  html{scroll-behavior:auto}
  .photon-in,.ir{animation:none}
}