/* Shell Nav */
.shell-nav{position:fixed;top:0;left:0;right:0;z-index:2000;background:rgba(26,26,46,0.85);backdrop-filter:blur(24px);-webkit-backdrop-filter:blur(24px);border-bottom:1px solid rgba(255,255,255,0.06);transition:all 0.4s cubic-bezier(0.16,1,0.3,1)}
.shell-nav.scrolled{background:rgba(15,15,26,0.96);box-shadow:0 4px 30px rgba(0,0,0,0.5)}
.nav-inner{max-width:1280px;margin:0 auto;display:flex;align-items:center;justify-content:space-between;padding:0 32px;height:64px}
.nav-brand{display:flex;align-items:center;gap:12px;text-decoration:none;font-weight:700;font-size:17px;color:#f0f0f0}
.nav-brand .brand-icon{width:34px;height:34px;background:linear-gradient(135deg,#7DB6B1,#5a9e98);border-radius:10px;display:flex;align-items:center;justify-content:center;font-size:15px;font-weight:900;color:#0f0f1a}
.nav-brand span{color:#7DB6B1}
.nav-links{display:flex;align-items:center;gap:4px}
.nav-link{padding:8px 16px;border-radius:8px;text-decoration:none;font-size:14px;font-weight:600;color:#9ca3af}
.nav-link:hover{color:#f0f0f0;background:rgba(255,255,255,0.04)}
.nav-cta{padding:8px 24px;border-radius:8px;background:linear-gradient(135deg,#7DB6B1,#5a9e98);color:#0f0f1a;text-decoration:none;font-size:14px;font-weight:700;display:inline-block}
.nav-cta:hover{transform:translateY(-1px);box-shadow:0 4px 20px rgba(125,182,177,0.25)}
.nav-progress{position:absolute;bottom:-2px;left:0;height:2px;background:linear-gradient(90deg,#7DB6B1,#a3d4cf);width:0%;transition:width 0.1s linear}
.breadcrumbs{display:flex;align-items:center;gap:8px;padding:80px 32px 8px;max-width:1280px;margin:0 auto;font-size:13px;color:#6b7280}
.breadcrumbs a{color:#9ca3af;text-decoration:none}
.breadcrumbs a:hover{color:#7DB6B1}
.breadcrumbs .current{color:#1e293b;font-weight:600}
.breadcrumbs .separator{margin:0 2px}
:root{
  --pri:#2563eb;--pri-dk:#1d4ed8;--pri-lt:#3b82f6;--sec:#60a5fa;--acc:#93c5fd;
  --ok:#10b981;--warn:#f59e0b;--err:#ef4444;--info:#3b82f6;
  --w:#fff;--g50:#f9fafb;--g100:#f3f4f6;--g200:#e5e7eb;--g300:#d1d5db;--g400:#9ca3af;--g500:#6b7280;--g600:#4b5563;--g700:#374151;--g800:#1f2937;--g900:#111827;
  --font:'Inter',-apple-system,BlinkMacSystemFont,'Segoe UI',sans-serif;
  --r-sm:.375rem;--r-md:.5rem;--r-lg:.75rem;--r-xl:1rem;
  --sh-sm:0 1px 2px rgba(0,0,0,.05);--sh-md:0 4px 6px -1px rgba(0,0,0,.1);--sh-lg:0 10px 15px -3px rgba(0,0,0,.1);--sh-xl:0 20px 25px -5px rgba(0,0,0,.1);
  --tr:.3s ease;
}
*{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth}
body{font-family:var(--font);line-height:1.6;color:var(--g800);background:linear-gradient(135deg,#667eea,#764ba2);min-height:100vh}
/* NAV */
.topnav{position:sticky;top:0;z-index:1000;background:rgba(30,30,60,.95);backdrop-filter:blur(12px);padding:.6rem 1rem;display:flex;align-items:center;gap:.5rem;flex-wrap:wrap;box-shadow:0 2px 12px rgba(0,0,0,.3)}
.topnav .brand{color:#fff;font-weight:700;font-size:1.1rem;margin-right:auto;white-space:nowrap}
.topnav a{color:rgba(255,255,255,.8);text-decoration:none;font-size:.82rem;padding:.35rem .65rem;border-radius:var(--r-sm);transition:var(--tr)}
.topnav a:hover{background:rgba(255,255,255,.15);color:#fff}
.ham{display:none;background:none;border:none;color:#fff;font-size:1.5rem;cursor:pointer}
@media(max-width:768px){.ham{display:block}.nav-links{display:none;width:100%;flex-direction:column}.nav-links.open{display:flex}}
/* CONTAINER */
.container{max-width:1100px;margin:0 auto;padding:1.5rem}
h1{font-size:2.6rem;font-weight:700;color:#fff;text-align:center;margin:1.5rem 0 2rem;text-shadow:0 4px 8px rgba(0,0,0,.3)}
/* CARD */
.card{background:var(--w);border-radius:var(--r-xl);box-shadow:var(--sh-lg);padding:2rem;margin-bottom:2rem;border-top:4px solid var(--pri);opacity:0;transform:translateY(30px);transition:opacity .6s ease,transform .6s ease}
.card.vis{opacity:1;transform:translateY(0)}
.card:hover{box-shadow:var(--sh-xl)}
h2{font-size:1.7rem;font-weight:600;color:var(--pri);margin-bottom:1rem;display:flex;align-items:center;gap:.5rem}
h2 .icon{width:42px;height:42px;background:linear-gradient(135deg,#667eea,#764ba2);border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:1.2rem;flex-shrink:0}
h3{font-size:1.3rem;font-weight:600;color:var(--pri-dk);margin:1.2rem 0 .6rem}
h4{font-size:1.1rem;font-weight:500;color:var(--g700);margin:.8rem 0 .5rem}
p{margin-bottom:.7rem}
ul,ol{margin-bottom:.7rem;padding-left:1.5rem}
li{margin-bottom:.3rem}
strong{color:var(--g900)}
/* BOXES */
.lo{background:linear-gradient(135deg,#eef7ff,#dbeafe);border:1px solid var(--acc);border-radius:var(--r-lg);padding:1.2rem;margin-bottom:1rem}
.lo h4{color:var(--pri);margin-top:0}
.formula{background:linear-gradient(135deg,#e0f2fe,#b3e5fc);padding:1.2rem;border-radius:var(--r-lg);border-left:4px solid var(--pri);text-align:center;font-weight:600;margin:1rem 0;box-shadow:var(--sh-sm)}
.example{background:linear-gradient(135deg,#fefce8,#fef3c7);border-left:4px solid var(--warn);border-radius:var(--r-lg);padding:1.2rem;margin:1rem 0}
.pnote{background:linear-gradient(135deg,#f0fdf4,#dcfce7);border-left:4px solid var(--ok);border-radius:var(--r-lg);padding:1.2rem;margin:1rem 0}
.explanation{font-style:italic;color:var(--g600);padding:.5rem;background:rgba(107,114,128,.05);border-radius:var(--r-md);border-left:3px solid var(--g400);margin:.5rem 0}
/* FORM */
input[type=number],select{width:100%;padding:.6rem;border:2px solid var(--g200);border-radius:var(--r-md);font:1rem var(--font);transition:var(--tr);margin-top:.3rem}
input[type=number]:focus,select:focus{outline:none;border-color:var(--pri);box-shadow:0 0 0 3px rgba(37,99,235,.1)}
label{font-weight:500;color:var(--g700);font-size:.9rem}
/* BUTTON */
.btn{background:linear-gradient(135deg,#667eea,#764ba2);color:#fff;border:none;padding:.6rem 1.3rem;border-radius:var(--r-md);font:500 .95rem var(--font);cursor:pointer;transition:var(--tr);box-shadow:var(--sh-md);display:inline-flex;align-items:center;gap:.4rem}
.btn:hover{transform:translateY(-2px);box-shadow:var(--sh-lg)}
.btn:active{transform:translateY(0)}
.btn-ok{background:linear-gradient(135deg,#11998e,#38ef7d)}
.btn-warn{background:linear-gradient(135deg,#f59e0b,#fbbf24);color:var(--g800)}
.btn-err{background:linear-gradient(135deg,#ef4444,#f87171)}
/* RESULT */
.result{background:linear-gradient(135deg,#11998e,#38ef7d);color:#fff;padding:1rem;border-radius:var(--r-md);font-weight:600;margin-top:1rem;opacity:0;transform:translateX(-20px);transition:var(--tr)}
.result.show{opacity:1;transform:translateX(0)}
/* GRID */
.grid2{display:grid;grid-template-columns:1fr 1fr;gap:1rem;margin:.8rem 0}
@media(max-width:600px){.grid2{grid-template-columns:1fr}}
/* SIM */
.sim-wrap{background:var(--g50);border-radius:var(--r-lg);padding:1.2rem;margin:1rem 0;border:1px solid var(--g200)}
.sim-wrap h4{margin-top:0;color:var(--pri)}
.sim-controls{display:flex;flex-wrap:wrap;gap:.6rem;align-items:center;margin:.6rem 0}
.sim-controls label{display:flex;align-items:center;gap:.4rem;font-size:.85rem}
.sim-controls input[type=range]{width:120px;accent-color:var(--pri)}
canvas{display:block;width:100%;border-radius:var(--r-md);background:#f8fafc;box-shadow:var(--sh-sm)}
.energy-bars{display:flex;gap:1rem;flex-wrap:wrap;margin-top:.6rem}
.ebar{flex:1;min-width:100px}
.ebar-label{font-size:.75rem;font-weight:600;margin-bottom:.2rem;display:flex;justify-content:space-between}
.ebar-track{height:16px;background:var(--g200);border-radius:10px;overflow:hidden}
.ebar-fill{height:100%;border-radius:10px;transition:width .05s linear}
.fill-gpe{background:linear-gradient(90deg,#10b981,#34d399)}
.fill-ke{background:linear-gradient(90deg,#f59e0b,#fbbf24)}
.fill-th{background:linear-gradient(90deg,#ef4444,#f87171)}
.fill-tot{background:linear-gradient(90deg,#8b5cf6,#a78bfa)}
/* SVG DIAGRAMS */
.diagram{background:var(--w);border-radius:var(--r-lg);padding:1rem;margin:1rem 0;border:1px solid var(--g200);text-align:center}
.diagram svg{max-width:100%;height:auto}
/* QUIZ */
.quiz-q{background:var(--w);padding:1rem;border-radius:var(--r-md);margin-bottom:1rem;border-left:4px solid var(--pri);box-shadow:var(--sh-sm);transition:var(--tr)}
.quiz-q.correct{border-left-color:var(--ok);background:#f0fdf4}
.quiz-q.wrong{border-left-color:var(--err);background:#fef2f2}
.quiz-q label{display:block;padding:.3rem .5rem;border-radius:var(--r-sm);cursor:pointer;font-size:.9rem;transition:var(--tr)}
.quiz-q label:hover{background:var(--g50)}
.quiz-q input[type=radio]{margin-right:.4rem;accent-color:var(--pri)}
/* SANKEY */
#sankey-svg{width:100%;max-width:550px;margin:1rem auto;display:block}
/* WORKING OUT */
.wo{background:linear-gradient(135deg,#f8fafc,#e2e8f0);border-radius:var(--r-lg);padding:1.2rem;margin-top:1rem;border-top:3px solid var(--sec)}
.wo-step{background:var(--w);border-radius:var(--r-md);padding:.8rem;margin-bottom:.6rem;border-left:4px solid var(--sec);box-shadow:var(--sh-sm)}
.wo-step .num{display:inline-flex;align-items:center;justify-content:center;width:24px;height:24px;background:linear-gradient(135deg,#667eea,#764ba2);color:#fff;border-radius:50%;font-size:.75rem;font-weight:700;margin-right:.5rem}
.wo-calc{font-family:monospace;background:var(--g50);padding:.5rem;border-radius:var(--r-sm);border:1px solid var(--g200);margin:.3rem 0;font-size:.95rem}
.wo-final{background:linear-gradient(135deg,#11998e,#38ef7d);color:#fff;padding:1rem;border-radius:var(--r-lg);text-align:center;font-size:1.1rem;font-weight:700;margin-top:.8rem}
/* TABLE */
.ins-table{width:100%;border-collapse:collapse;margin:.8rem 0;font-size:.9rem}
.ins-table th{background:linear-gradient(135deg,#667eea,#764ba2);color:#fff;padding:.7rem;text-align:left}
.ins-table td{padding:.6rem;border-bottom:1px solid var(--g200)}
.ins-table tr:nth-child(even) td{background:var(--g50)}
.ins-table tr:hover td{background:#eef7ff}
/* FOOTER */
.foot{text-align:center;color:rgba(255,255,255,.7);padding:2rem;font-size:.85rem}
@media(prefers-reduced-motion:reduce){*,*::before,*::after{animation-duration:.01ms!important;transition-duration:.01ms!important}}
@media(max-width:600px){h1{font-size:1.8rem}.card{padding:1.2rem}h2{font-size:1.3rem;flex-wrap:wrap}}