:root{
  --ink:#16212c;
  --ink-soft:#42505d;
  --muted:#697682;
  --paper:#f5f7f9;
  --surface:#ffffff;
  --line:#dde3ea;
  --line-soft:#e9edf1;
  --marine:#0e7a8c;
  --marine-deep:#0a5461;
  --marine-wash:#e5f1f3;
  --amber:#b26608;
  --amber-wash:#fbf1e2;
  --green:#2e7d5b;
  --green-wash:#e7f2ec;
  --shadow:0 1px 2px rgba(20,33,44,.04), 0 8px 24px rgba(20,33,44,.05);
  --maxw:760px;
}
:root[data-theme="dark"]{
  --ink:#e8e8e8;
  --ink-soft:#b0b0b0;
  --muted:#7a7a7a;
  --paper:#0a0a0a;
  --surface:#161616;
  --line:#2a2a2a;
  --line-soft:#1e1e1e;
  --marine:#38b3c6;
  --marine-deep:#7ad2e0;
  --marine-wash:#132c30;
  --amber:#d98c33;
  --amber-wash:#2a2015;
  --green:#4cc08a;
  --green-wash:#132a22;
  --shadow:0 1px 2px rgba(0,0,0,.4), 0 10px 30px rgba(0,0,0,.5);
}
:root[data-theme="dark"] .d-plane{fill:#1a2b2f}
:root[data-theme="dark"] .d-node{fill:#1a1a1a}
:root[data-theme="dark"] .tag{background:#1f1f1f;border-color:#2e2e2e;color:var(--marine-deep)}


.theme-toggle{appearance:none;border:1px solid var(--line);background:var(--surface);color:var(--ink-soft);width:34px;height:34px;border-radius:9px;cursor:pointer;display:inline-flex;align-items:center;justify-content:center;flex:none;transition:color .15s ease,border-color .15s ease}
.theme-toggle:hover{color:var(--marine);border-color:var(--marine)}
.theme-toggle .sun{display:none}
.theme-toggle .moon{display:block}
:root[data-theme="dark"] .theme-toggle .moon{display:none}
:root[data-theme="dark"] .theme-toggle .sun{display:block}
.brand .theme-toggle{margin-left:auto}
.topbar .theme-toggle{margin-left:auto}

*{box-sizing:border-box}
html{scroll-behavior:smooth}
@media (prefers-reduced-motion: reduce){html{scroll-behavior:auto}}
body{
  margin:0;
  background:var(--paper);
  color:var(--ink);
  font-family:"IBM Plex Sans",system-ui,sans-serif;
  font-size:17px;
  line-height:1.65;
  -webkit-font-smoothing:antialiased;
}

/* Layout */
.shell{display:grid;grid-template-columns:288px minmax(0,1fr);}
@media (max-width:960px){.shell{grid-template-columns:1fr}}

/* Sidebar */
.sidebar{
  position:sticky;top:0;align-self:start;height:100vh;
  border-right:1px solid var(--line);
  background:var(--surface);
  padding:34px 26px 40px;
  overflow-y:auto;
}
.brand{display:flex;align-items:flex-start;gap:12px;margin-bottom:6px}
.brand-stack{flex:1;min-width:0}
.brand-eyebrow{font-family:"IBM Plex Mono";font-size:10.5px;font-weight:600;letter-spacing:.18em;text-transform:uppercase;color:var(--marine);margin-bottom:8px;line-height:1}
.brand-wordmark{display:block;width:100%;max-width:160px;height:auto}
:root[data-theme="dark"] .brand-wordmark.light{display:none}
:root[data-theme="dark"] .brand-wordmark.dark{display:block}
.brand-wordmark.dark{display:none}
.brand-sub{font-family:"IBM Plex Mono";font-size:10px;letter-spacing:.14em;text-transform:uppercase;color:var(--muted);margin-top:8px;line-height:1}
.brand-title{font-family:"Space Grotesk";font-weight:600;font-size:16px;line-height:1.2;letter-spacing:-.01em}
.nav{margin-top:26px}
.nav a{
  display:flex;gap:12px;align-items:baseline;
  text-decoration:none;color:var(--ink-soft);
  padding:7px 10px;border-radius:7px;margin:1px 0;
  font-size:14px;line-height:1.35;
  transition:background .15s ease,color .15s ease;
}
.nav a .num{font-family:"IBM Plex Mono";font-size:11px;color:var(--muted);flex:none;width:20px}
.nav a:hover{background:var(--paper);color:var(--ink)}
.nav a.active{background:var(--marine-wash);color:var(--marine-deep);font-weight:500}
.nav a.active .num{color:var(--marine)}
.nav-part{font-family:"IBM Plex Mono";font-size:10px;letter-spacing:.16em;text-transform:uppercase;color:var(--muted);margin:22px 0 6px 10px}
.nav-part:first-of-type{margin-top:8px}

/* Mobile top bar */
.topbar{display:none}
@media (max-width:960px){
  .sidebar{display:none;position:fixed;z-index:40;width:min(320px,86vw);height:100vh;box-shadow:var(--shadow)}
  .sidebar.open{display:block}
  .topbar{
    display:flex;align-items:center;gap:12px;position:sticky;top:0;z-index:30;
    background:var(--surface);border-bottom:1px solid var(--line);
    padding:12px 16px;
  }
  .topbar .brand-title{font-size:14px}
  .menu-btn{
    appearance:none;border:1px solid var(--line);background:var(--surface);
    border-radius:8px;padding:8px 10px;cursor:pointer;color:var(--ink);
    font-family:"IBM Plex Mono";font-size:12px;display:flex;align-items:center;gap:7px;
  }
  .scrim{display:none;position:fixed;inset:0;background:rgba(20,33,44,.34);z-index:35}
  .scrim.open{display:block}
}

/* Content */
main{padding:0}
.wrap{max-width:var(--maxw);margin:0 auto;padding:0 28px}
@media (max-width:960px){.wrap{padding:0 22px}}

/* Hero */
.hero{padding:76px 0 52px;border-bottom:1px solid var(--line)}
.eyebrow{font-family:"IBM Plex Mono";font-size:12px;letter-spacing:.18em;text-transform:uppercase;color:var(--marine);margin-bottom:20px}
h1{
  font-family:"Space Grotesk";font-weight:700;
  font-size:clamp(32px,5vw,50px);line-height:1.05;letter-spacing:-.02em;
  margin:0 0 20px;color:var(--ink);
}
.lede{font-size:19px;line-height:1.6;color:var(--ink-soft);max-width:58ch}
.hero-meta{margin-top:26px;display:flex;flex-wrap:wrap;gap:10px}
.chip{
  font-family:"IBM Plex Mono";font-size:11.5px;letter-spacing:.04em;
  color:var(--ink-soft);background:var(--surface);border:1px solid var(--line);
  padding:5px 11px;border-radius:100px;
}

section{padding:52px 0;border-bottom:1px solid var(--line-soft)}
section:last-of-type{border-bottom:none}
.sec-head{display:flex;align-items:baseline;gap:14px;margin-bottom:8px}
.sec-num{font-family:"IBM Plex Mono";font-weight:600;font-size:13px;color:var(--marine);flex:none;padding-top:6px}
h2{
  font-family:"Space Grotesk";font-weight:600;
  font-size:clamp(23px,3.2vw,30px);line-height:1.15;letter-spacing:-.015em;
  margin:0;color:var(--ink);
}
h3{
  font-family:"Space Grotesk";font-weight:600;font-size:19px;letter-spacing:-.01em;
  margin:32px 0 6px;color:var(--ink);
}
p{margin:0 0 18px}
section p:first-of-type{margin-top:14px}
strong{font-weight:600;color:var(--ink)}
.tag{
  font-family:"IBM Plex Mono";font-size:.86em;font-weight:500;
  background:#eef2f5;color:var(--marine-deep);
  padding:1px 6px;border-radius:5px;border:1px solid #e2e8ec;
  white-space:nowrap;
}

/* Callouts */
.callout{
  border:1px solid var(--line);border-radius:10px;
  background:var(--surface);padding:18px 20px;margin:26px 0;box-shadow:var(--shadow);
}
.callout .k{
  font-family:"IBM Plex Mono";font-size:11px;letter-spacing:.14em;text-transform:uppercase;
  display:flex;align-items:center;gap:8px;margin-bottom:8px;font-weight:600;
}
.callout p:last-child{margin-bottom:0}
.callout.principle .k{color:var(--marine)}
.callout.edge{background:var(--amber-wash)}
.callout.edge .k{color:var(--amber)}
.callout.lab{background:var(--green-wash)}
.callout.lab .k{color:var(--green)}
.dot{width:8px;height:8px;border-radius:50%;flex:none}
.dot.tl{background:var(--marine)}
.dot.am{background:var(--amber)}
.dot.gr{background:var(--green)}

/* Figures */
figure{margin:30px 0;background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:22px 20px 16px;box-shadow:var(--shadow)}
figure svg{display:block;width:100%;height:auto}
figcaption{font-size:13.5px;color:var(--muted);margin-top:14px;text-align:center;font-family:"IBM Plex Mono";letter-spacing:.01em}

/* Matrix (keep vs stop) */
.matrix{display:grid;grid-template-columns:1fr 1fr;gap:14px;margin:26px 0}
@media (max-width:560px){.matrix{grid-template-columns:1fr}}
.matrix .col{border:1px solid var(--line);border-radius:11px;padding:16px 18px;background:var(--surface);box-shadow:var(--shadow)}
.matrix .col.keep{border-top:3px solid var(--green)}
.matrix .col.stop{border-top:3px solid var(--amber)}
.matrix .col h4{font-family:"Space Grotesk";font-size:14px;margin:0 0 11px;display:flex;align-items:center;gap:8px}
.matrix .col.keep h4{color:var(--green)}
.matrix .col.stop h4{color:var(--amber)}
.matrix ul{margin:0;padding-left:18px;font-size:14px;line-height:1.5;color:var(--ink-soft)}
.matrix li{margin:0 0 7px}
.matrix li:last-child{margin-bottom:0}

/* Resource table */
table.rt{width:100%;border-collapse:collapse;margin:24px 0;font-size:14.5px}
table.rt caption{font-family:"IBM Plex Mono";font-size:10.5px;letter-spacing:.1em;text-transform:uppercase;color:var(--marine);text-align:left;margin-bottom:10px}
table.rt th,table.rt td{text-align:left;padding:10px 12px;border-bottom:1px solid var(--line-soft);vertical-align:top}
table.rt thead th{font-family:"IBM Plex Mono";font-size:11px;letter-spacing:.05em;text-transform:uppercase;color:var(--muted);font-weight:600;border-bottom:1px solid var(--line)}
table.rt tbody th{font-weight:600;color:var(--ink)}
table.rt tr:last-child td,table.rt tr:last-child th{border-bottom:none}
@media (max-width:560px){table.rt{font-size:12.5px}table.rt th,table.rt td{padding:8px 7px}}

/* SVG shared classes */
.d-box{fill:var(--surface);stroke:var(--line);stroke-width:1.5}
.d-plane{fill:#f0f6f7;stroke:var(--marine);stroke-width:1.5;stroke-dasharray:0}
.d-node{fill:#fbfcfd;stroke:var(--line);stroke-width:1.5}
.d-accent{fill:var(--marine)}
.d-accent-soft{fill:var(--marine-wash);stroke:var(--marine);stroke-width:1.5}
.d-amber{fill:var(--amber-wash);stroke:var(--amber);stroke-width:1.5}
.d-green{fill:var(--green-wash);stroke:var(--green);stroke-width:1.5}
.d-line{stroke:var(--muted);stroke-width:1.5;fill:none}
.d-line-accent{stroke:var(--marine);stroke-width:1.75;fill:none}
.t-lab{font-family:"IBM Plex Mono";font-size:12px;fill:var(--ink);font-weight:500}
.t-lab-w{font-family:"IBM Plex Mono";font-size:12px;fill:#fff;font-weight:500}
.t-sub{font-family:"IBM Plex Sans";font-size:11px;fill:var(--muted)}
.t-cap{font-family:"IBM Plex Mono";font-size:10.5px;fill:var(--marine);letter-spacing:.08em;font-weight:600}
.t-title{font-family:"Space Grotesk";font-size:13px;fill:var(--ink);font-weight:600}
.flow-dot{pointer-events:none}
@media (prefers-reduced-motion: reduce){ .flow-dot{display:none} }

.footer{padding:48px 0 80px;color:var(--muted);font-size:13.5px}
.footer a{color:var(--marine-deep)}

a.inline{color:var(--marine-deep);text-decoration:underline;text-underline-offset:2px;text-decoration-thickness:1px}

::selection{background:var(--marine-wash)}

/* Module switcher */
.lessons{margin-top:24px;padding-bottom:16px;border-bottom:1px solid var(--line-soft)}
.lessons a.cur{background:var(--marine-wash);color:var(--marine-deep);font-weight:500}
.lessons a.cur .num{color:var(--marine)}
.lessons a .num.aside{color:var(--marine);font-size:13px;line-height:1}

/* Welcome page bits */
.roadmap{margin:26px 0}
.roadmap .item{
  display:grid;grid-template-columns:44px 1fr;gap:14px;align-items:baseline;
  padding:14px 0;border-bottom:1px solid var(--line-soft);
}
.roadmap .item:last-child{border-bottom:none}
.roadmap .item .n{font-family:"IBM Plex Mono";font-size:12px;color:var(--marine);font-weight:600;padding-top:3px}
.roadmap .item h4{font-family:"Space Grotesk";font-size:16px;font-weight:600;margin:0 0 4px;color:var(--ink)}
.roadmap .item p{margin:0;font-size:14.5px;color:var(--ink-soft);line-height:1.55}

.cta{
  display:inline-flex;align-items:center;gap:10px;
  background:var(--marine);color:#fff;
  padding:13px 22px;border-radius:9px;font-family:"IBM Plex Mono";font-size:13.5px;
  letter-spacing:.04em;text-decoration:none;
  transition:background .15s ease;
  margin-top:12px;
}
.cta:hover{background:var(--marine-deep)}
.cta svg{width:14px;height:14px}