@import url('https://fonts.googleapis.com/css2?family=Space+Grotesk:wght@400;500;600;700&display=swap');

:root{--font:'Space Grotesk',system-ui,-apple-system,'Segoe UI',sans-serif;--max:1220px;--accent:#fbbf24;--button-ink:#151825;--ink:#edf2ff;--muted:#a9b4cf;--bg:#090e1c;--surface:#111a30;--surface-2:#15203a;--line:rgba(173,188,220,.19);--paper:#e9edf5;--shadow:0 24px 70px rgba(0,0,0,.32);color-scheme:dark}
:root[data-theme=light]{--accent:#9d5204;--button-ink:#ffffff;--ink:#172238;--muted:#52617b;--bg:#f4f6fb;--surface:#fff;--surface-2:#edf1f8;--line:rgba(35,55,84,.19);--paper:#e9edf5;--shadow:0 20px 50px rgba(30,48,78,.12);color-scheme:light}
*{box-sizing:border-box}html{scroll-behavior:smooth;scroll-padding-top:90px}body{margin:0;background:var(--bg);color:var(--ink);font:400 16px/1.65 var(--font);overflow-x:hidden}a{color:inherit}button{font:inherit}img{max-width:100%;display:block}svg{display:block}h1,h2,h3,p{margin:0}h1,h2,h3{line-height:1.13;text-wrap:balance}p{max-width:75ch}ul{margin:0;padding:0}li{list-style:none}::selection{background:var(--accent);color:var(--bg)}:focus-visible{outline:3px solid var(--accent);outline-offset:4px;border-radius:5px}
html[lang=fr] [lang=en],html[lang=en] [lang=fr]{display:none!important}
.container{width:min(var(--max),calc(100% - 48px));margin-inline:auto}.skip{position:absolute;z-index:100;top:-90px;left:16px;padding:10px 14px;border-radius:10px;background:var(--accent);color:var(--button-ink);font-weight:700}.skip:focus{top:12px}
.progress{position:fixed;z-index:100;top:0;left:0;width:100%;height:3px;transform:scaleX(0);transform-origin:left;background:var(--accent);pointer-events:none}
.topbar{position:sticky;top:0;z-index:50;border-bottom:1px solid var(--line);background:color-mix(in srgb,var(--bg) 88%,transparent);backdrop-filter:blur(18px)}.topbar-inner{width:min(var(--max),calc(100% - 48px));margin:auto;min-height:70px;display:flex;align-items:center;gap:20px}.mark{width:37px;height:37px;border-radius:11px;background:#111b2f;color:#fbbf24;display:grid;place-items:center;flex:none;font-weight:700;font-size:19px;box-shadow:inset 0 0 0 1px rgba(251,191,36,.3)}.brand{display:flex;align-items:center;gap:10px;text-decoration:none;font-size:.94rem;font-weight:700;white-space:nowrap}.brand span:last-child{color:var(--accent)}.topbar-title{margin-right:auto;padding-left:18px;border-left:1px solid var(--line);color:var(--muted);font-size:.84rem;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}.top-actions{display:flex;gap:8px}.icon-btn{min-width:43px;min-height:43px;border:1px solid var(--line);border-radius:11px;background:var(--surface);color:var(--ink);cursor:pointer;font-weight:700}.icon-btn:hover{border-color:var(--accent);color:var(--accent)}
.hero{position:relative;isolation:isolate;overflow:hidden;padding:86px 0 86px;background:radial-gradient(circle at 83% 18%,rgba(251,191,36,.09),transparent 28%),linear-gradient(145deg,var(--bg),var(--surface))}.hero:before{content:'';position:absolute;z-index:-1;inset:0;background-image:linear-gradient(var(--line) 1px,transparent 1px),linear-gradient(90deg,var(--line) 1px,transparent 1px);background-size:42px 42px;opacity:.26;mask-image:linear-gradient(to right,transparent 15%,#000 100%)}.hero-grid{display:grid;grid-template-columns:minmax(0,1.03fr) minmax(0,.97fr);align-items:center;gap:clamp(28px,6vw,86px)}.eyebrow{display:flex;align-items:center;gap:10px;color:var(--accent);font-size:.82rem;font-weight:700;letter-spacing:.14em;text-transform:uppercase}.eyebrow:before{content:'';width:30px;height:1px;background:currentColor}.hero h1{margin:19px 0 25px;font-size:clamp(2.9rem,5.5vw,5.8rem);letter-spacing:-.055em}.hero h1 em{font-style:normal;color:var(--accent)}.lede{font-size:clamp(1.08rem,1.4vw,1.32rem);color:var(--muted);line-height:1.58}.hero-actions{display:flex;flex-wrap:wrap;gap:11px;margin-top:29px}.button{display:inline-flex;align-items:center;justify-content:center;gap:9px;min-height:47px;padding:10px 17px;border-radius:11px;border:1px solid var(--line);text-decoration:none;font-weight:700;font-size:.91rem;transition:transform .2s,border-color .2s,background .2s}.button:hover{transform:translateY(-2px);border-color:var(--accent)}.button.primary{background:var(--accent);border-color:var(--accent);color:var(--button-ink)}.button.ghost{background:var(--surface)}.hero-art{margin:0;position:relative;border:1px solid var(--line);border-radius:24px;background:var(--surface-2);padding:12px;box-shadow:var(--shadow);transform:rotate(1deg)}.hero-art:after{content:'';position:absolute;z-index:-1;inset:20px -20px -20px 20px;border:1px solid var(--accent);border-radius:24px;opacity:.45}.hero-art img{width:100%;height:clamp(280px,31vw,435px);object-fit:contain;background:var(--paper);border-radius:16px}.hero-art figcaption{display:flex;justify-content:space-between;gap:16px;padding:12px 7px 4px;color:var(--muted);font-size:.8rem}.hero-art small{color:var(--accent);font-weight:700;letter-spacing:.1em}.hero-index{margin-top:38px;display:flex;flex-wrap:wrap;gap:9px}.hero-index>span{border:1px solid var(--line);padding:5px 11px;border-radius:999px;color:var(--muted);font-size:.76rem;letter-spacing:.04em}
.metric-band{border-top:1px solid var(--line);border-bottom:1px solid var(--line);background:var(--surface)}.metrics{display:grid;grid-template-columns:repeat(3,minmax(0,1fr))}.metric{padding:28px 22px;border-right:1px solid var(--line)}.metric:first-child{padding-left:0}.metric:last-child{border:0}.metric strong{display:block;color:var(--accent);font-size:clamp(1.6rem,2.8vw,2.4rem);line-height:1.1;letter-spacing:-.04em}.metric>span{display:block;margin-top:7px;color:var(--muted);font-size:.83rem}
.story-shell{display:grid;grid-template-columns:185px minmax(0,1fr);gap:clamp(28px,6vw,95px);padding-block:75px 105px}.chapter-nav{position:sticky;top:105px;align-self:start}.chapter-nav p{font-size:.7rem;letter-spacing:.16em;color:var(--muted);font-weight:700;text-transform:uppercase}.chapter-nav ol{margin:20px 0 0;padding:0;border-left:1px solid var(--line)}.chapter-nav li{margin:0}.chapter-nav a{display:block;margin-left:-1px;padding:9px 0 9px 16px;border-left:2px solid transparent;color:var(--muted);font-size:.82rem;text-decoration:none}.chapter-nav a:hover,.chapter-nav a[aria-current=true]{border-color:var(--accent);color:var(--accent)}.story{min-width:0}.chapter{padding:0 0 77px;margin:0 0 72px;border-bottom:1px solid var(--line)}.chapter:last-child{margin-bottom:0;border-bottom:0}.chapter-head{display:flex;align-items:center;gap:16px;margin-bottom:23px}.chapter-no{color:var(--accent);font-size:.8rem;font-weight:700;letter-spacing:.16em}.chapter-head:after{content:'';width:46px;height:1px;background:var(--accent);opacity:.7}.chapter h2{font-size:clamp(2rem,3.5vw,3.4rem);letter-spacing:-.04em;max-width:18ch}.chapter .intro{margin-top:21px;font-size:1.16rem;color:var(--ink);line-height:1.7}.prose{display:grid;gap:20px;margin-top:23px;color:var(--muted)}.prose p{line-height:1.78}.key-points{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:12px;margin-top:30px}.key-point{border:1px solid var(--line);border-radius:14px;padding:20px;background:var(--surface)}.key-point b{display:block;color:var(--accent);font-size:.79rem;letter-spacing:.09em;text-transform:uppercase;margin-bottom:12px}.key-point p{color:var(--muted);font-size:.91rem;line-height:1.55}.figure{margin:37px 0 0;border:1px solid var(--line);border-radius:18px;padding:10px;background:var(--surface);overflow:hidden}.figure img{width:100%;max-height:500px;object-fit:contain;background:var(--paper);border-radius:11px}.figure figcaption{display:flex;align-items:baseline;gap:12px;padding:14px 8px 5px;color:var(--muted);font-size:.82rem}.figure figcaption strong{color:var(--accent);white-space:nowrap;font-size:.72rem;letter-spacing:.08em}.figure-link{display:block;text-decoration:none}.figure-link:hover img{filter:brightness(.97)}.artifact-row{display:flex;flex-wrap:wrap;gap:10px;margin-top:27px}.artifact-row a{display:inline-flex;align-items:center;min-height:42px;padding:8px 13px;border:1px solid var(--line);border-radius:9px;color:var(--ink);font-size:.84rem;font-weight:600;text-decoration:none}.artifact-row a:hover{border-color:var(--accent);color:var(--accent)}.artifact-row a:after{content:'↗';margin-left:9px;color:var(--accent)}.source-note{font-size:.82rem;color:var(--muted);margin-top:18px}.source-note strong{color:var(--ink)}
.next{padding:68px 0;background:var(--surface);border-top:1px solid var(--line)}.next-inner{display:flex;justify-content:space-between;align-items:center;gap:24px}.next-kicker{font-size:.72rem;color:var(--accent);text-transform:uppercase;letter-spacing:.15em;font-weight:700}.next h2{font-size:clamp(1.7rem,3vw,3rem);letter-spacing:-.04em;margin-top:8px}.footer{padding:28px 0;color:var(--muted);font-size:.83rem}.footer-inner{display:flex;justify-content:space-between;flex-wrap:wrap;gap:16px}.footer a{color:var(--ink);text-decoration:none}.footer a:hover{color:var(--accent)}
@media(max-width:900px){.hero-grid{grid-template-columns:minmax(0,1fr)}.hero-art{width:min(100%,700px);transform:none}.hero-art img{height:clamp(260px,48vw,420px)}.story-shell{grid-template-columns:minmax(0,1fr);padding-top:40px}.chapter-nav{position:sticky;top:70px;z-index:20;min-width:0;max-width:100%;overflow:hidden;background:var(--bg);border-bottom:1px solid var(--line);padding:10px 0}.chapter-nav p{display:none}.chapter-nav ol{display:flex;gap:4px;margin:0;max-width:100%;overflow-x:auto;overflow-y:hidden;border:0;scrollbar-width:thin}.chapter-nav li{flex:none}.chapter-nav a{margin:0;border:0;border-radius:7px;padding:8px 11px;white-space:nowrap}.chapter-nav a[aria-current=true]{background:var(--surface);border:0}.topbar-title{display:none}.brand{margin-right:auto}}
@media(max-width:620px){.container,.topbar-inner{width:min(100% - 30px,var(--max))}.topbar-inner{min-height:62px}.brand{font-size:.84rem}.mark{width:34px;height:34px}.hero{padding:57px 0 65px}.hero h1{font-size:clamp(2.5rem,11vw,4rem)}.hero-art img{height:265px}.metrics{grid-template-columns:1fr}.metric,.metric:first-child{padding:16px 0;border-right:0;border-bottom:1px solid var(--line)}.metric:last-child{border:0}.metric strong{font-size:1.55rem}.story-shell{padding-bottom:30px}.chapter{padding-bottom:55px;margin-bottom:55px}.chapter h2{font-size:2rem}.key-points{grid-template-columns:1fr}.figure figcaption{display:block}.figure figcaption strong{display:block;margin-bottom:5px}.next-inner{align-items:flex-start;flex-direction:column}}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}.button{transition:none}.button:hover{transform:none}}

@media(prefers-reduced-motion:no-preference){.hero-art:after{animation:frame-pulse 6s ease-in-out infinite}}
@keyframes frame-pulse{50%{opacity:.2;transform:translate(3px,3px)}}

/* Phone and tablet reading: compact chapters, comfortable taps and safe edges. */
:root{--topbar-height:70px;--chapter-bar-height:65px;--safe-top:env(safe-area-inset-top,0px)}
body{padding-left:env(safe-area-inset-left,0px);padding-right:env(safe-area-inset-right,0px)}
.topbar{padding-top:var(--safe-top)}
.brand{min-height:44px}
.icon-btn{min-width:44px;min-height:44px;touch-action:manipulation}
.artifact-row a,.skip{min-height:44px;align-items:center}
.skip{display:inline-flex}
.skip:focus{top:calc(12px + var(--safe-top))}
.chapter-label-short,.figure-zoom{display:none}
.footer{padding-bottom:calc(28px + env(safe-area-inset-bottom,0px))}
@media(max-width:900px){
  html{scroll-padding-top:calc(var(--topbar-height) + var(--safe-top) + var(--chapter-bar-height) + 17px)}
  .chapter-nav{top:calc(var(--topbar-height) + var(--safe-top) + 1px)}
  .chapter-nav a{display:flex;align-items:center;min-height:44px;touch-action:manipulation}
  .chapter-nav ol{overscroll-behavior-x:contain}
  .figure-zoom{display:flex;justify-content:flex-end;min-height:30px;padding:7px 5px 0;color:var(--accent);font-size:.75rem;font-weight:600;line-height:1.5}
  .figure-link:hover{text-decoration:none}
  .figure-link:focus-visible{outline-offset:3px}
}
@media(max-width:620px){
  :root{--topbar-height:62px}
  .topbar-inner{gap:12px}
  .top-actions{gap:6px}
  .hero{padding:35px 0 44px}
  .hero-grid{gap:26px}
  .eyebrow{font-size:.74rem;letter-spacing:.09em}
  .hero h1{margin:16px 0 18px;font-size:clamp(2.15rem,8.9vw,3.25rem);line-height:1.08;text-wrap:balance}
  .lede{font-size:1rem;line-height:1.65}
  .hero-actions{margin-top:22px;gap:9px}
  .hero-actions .button{flex:1 1 140px}
  .hero-index{margin-top:22px}
  .hero-index>span{font-size:.75rem;line-height:1.55;overflow-wrap:anywhere}
  .hero-art{padding:8px;border-radius:17px}
  .hero-art:after{inset:14px -8px -10px 14px;border-radius:17px}
  .hero-art img{height:auto;aspect-ratio:16/10;border-radius:11px}
  .hero-art figcaption{gap:9px;padding:10px 3px 3px;font-size:.75rem}
  .hero-art small{font-size:.7rem;white-space:nowrap}
  .chapter-nav{padding:10px 0}
  .chapter-nav ol{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:3px;overflow:visible}
  .chapter-nav li{min-width:0}
  .chapter-nav a{justify-content:center;padding:8px 2px;font-size:clamp(.7rem,2.9vw,.8rem);font-weight:600}
  .chapter-label-full{display:none}
  .chapter-label-short{display:inline}
  .chapter h2{font-size:clamp(1.8rem,7vw,2rem);line-height:1.16}
  .chapter .intro{font-size:1.05rem;line-height:1.7}
  .key-point{padding:18px}
  .figure{padding:8px;border-radius:14px}
  .figure figcaption{padding-inline:4px}
  .next{padding:45px 0}
}
@media(max-width:359px){
  .container,.topbar-inner{width:calc(100% - 28px)}
  .brand{font-size:.8rem;gap:8px}
  .mark{width:30px;height:30px;font-size:16px}
  .topbar-inner{gap:8px}
  .hero h1{font-size:2.05rem}
  .hero-art figcaption{flex-wrap:wrap}
}

/* Read the operating sequence before opening the calculation details. */
.flow-steps{margin:28px 0 0;padding:0;display:grid;gap:0;border-top:1px solid var(--line)}
.flow-steps>li{display:grid;grid-template-columns:38px minmax(0,1fr);gap:15px;padding:22px 0;border-bottom:1px solid var(--line)}
.flow-number{color:var(--accent);font-weight:700;font-size:.82rem;padding-top:3px;font-variant-numeric:tabular-nums}
.flow-steps h3{font-size:1.1rem;line-height:1.35;margin:0 0 7px;letter-spacing:-.015em;text-wrap:pretty}
.flow-steps p{color:var(--muted);font-size:.97rem;line-height:1.65}
.method-detail{margin-top:24px;color:var(--muted)}
.method-detail summary{cursor:pointer;color:var(--ink);font-weight:600;padding:12px 0}
.method-detail .prose{margin-top:12px}
.reference-links{margin-top:25px;color:var(--muted);font-size:.82rem;line-height:1.7}
.reference-links a{color:var(--accent);text-underline-offset:3px}
.figure-context img{height:auto;max-height:none}
@media(max-width:620px){.flow-steps>li{grid-template-columns:29px minmax(0,1fr);gap:10px;padding:19px 0}.flow-steps h3{font-size:1.05rem}}