[data-theme="dark"]{
  --bg:#040d1a;--bg2:#071528;
  --glass:rgba(255,255,255,0.04);--glass-border:rgba(255,255,255,0.09);
  --cyan:#00e5ff;--cyan-dim:rgba(0,229,255,0.12);
  --mint:#00ffb3;--mint-dim:rgba(0,255,179,0.12);
  --amber:#ffb700;--amber-dim:rgba(255,183,0,0.13);
  --purple:#b47aff;--purple-dim:rgba(180,122,255,0.12);
  --red:#ff4d6d;--red-dim:rgba(255,77,109,0.13);
  --text:#c8d8f0;--text-dim:#6888aa;--text-bright:#eaf4ff;
  --card-bg:rgba(255,255,255,0.04);--card-border:rgba(255,255,255,0.09);
  --card-hover:rgba(255,255,255,0.07);--orb-opacity:0.16;
  --input-bg:rgba(255,255,255,0.06);--input-border:rgba(255,255,255,0.12);
}
[data-theme="light"]{
  --bg:#f0f4fa;--bg2:#e4edf8;
  --glass:rgba(255,255,255,0.7);--glass-border:rgba(80,120,200,0.15);
  --cyan:#0080aa;--cyan-dim:rgba(0,128,170,0.1);
  --mint:#007a55;--mint-dim:rgba(0,122,85,0.1);
  --amber:#b07800;--amber-dim:rgba(176,120,0,0.1);
  --purple:#7040b0;--purple-dim:rgba(112,64,176,0.1);
  --red:#c0203a;--red-dim:rgba(192,32,58,0.1);
  --text:#1a2a44;--text-dim:#5a7090;--text-bright:#0a1830;
  --card-bg:rgba(255,255,255,0.82);--card-border:rgba(80,130,200,0.18);
  --card-hover:rgba(255,255,255,0.95);--orb-opacity:0.10;
  --input-bg:rgba(255,255,255,0.9);--input-border:rgba(80,130,200,0.25);
}
*{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth}
body{background:var(--bg);color:var(--text);font-family:'Inter',sans-serif;min-height:100vh;overflow-x:hidden;transition:background 0.4s,color 0.4s}
/* BG Effects */
.bg-canvas{position:fixed;inset:0;z-index:0;pointer-events:none;overflow:hidden}
.orb{position:absolute;border-radius:50%;filter:blur(100px);opacity:var(--orb-opacity);animation:drift 22s ease-in-out infinite alternate}
.orb1{width:700px;height:700px;background:var(--cyan);top:-250px;left:-200px}
.orb2{width:550px;height:550px;background:var(--mint);bottom:-150px;right:-150px;animation-delay:-8s}
.orb3{width:400px;height:400px;background:var(--purple);top:35%;left:50%;animation-delay:-15s}
@keyframes drift{from{transform:translate(0,0) scale(1)}to{transform:translate(60px,80px) scale(1.1)}}
.grid-overlay{position:fixed;inset:0;z-index:0;pointer-events:none;background-image:linear-gradient(rgba(0,229,255,0.025) 1px,transparent 1px),linear-gradient(90deg,rgba(0,229,255,0.025) 1px,transparent 1px);background-size:42px 42px}
[data-theme="light"] .grid-overlay{background-image:linear-gradient(rgba(0,80,150,0.04) 1px,transparent 1px),linear-gradient(90deg,rgba(0,80,150,0.04) 1px,transparent 1px)}
/* Layout */
.main{position:relative;z-index:1;max-width:960px;margin:0 auto;padding:2.5rem 1.5rem 5rem}
@media(min-width:768px){.main{padding:3.5rem 2rem 6rem}}
.topbar{display:flex;align-items:center;justify-content:space-between;margin-bottom:2.5rem;flex-wrap:wrap;gap:0.8rem}
.topbar-left{display:flex;align-items:center;gap:0.8rem;flex-wrap:wrap}
.ctrl-btn{display:flex;align-items:center;gap:0.5rem;font-family:'DM Mono',monospace;font-size:0.65rem;letter-spacing:0.08em;padding:0.42rem 0.9rem;border-radius:100px;border:1px solid var(--glass-border);background:var(--glass);color:var(--text-dim);cursor:pointer;transition:all 0.2s;backdrop-filter:blur(8px);white-space:nowrap;text-decoration:none}
.ctrl-btn:hover{border-color:var(--cyan);color:var(--cyan);background:var(--cyan-dim)}
.ctrl-btn svg{width:13px;height:13px;flex-shrink:0}
/* Hero */
.hero{text-align:center;margin-bottom:3.5rem;animation:heroIn 0.9s cubic-bezier(0.22,1,0.36,1) both}
@keyframes heroIn{from{opacity:0;transform:translateY(-28px)}to{opacity:1;transform:translateY(0)}}
.hero h1{font-size:clamp(2.1rem,5vw,3.2rem);font-weight:900;line-height:1.05;letter-spacing:-0.04em;color:var(--text-bright);margin-bottom:0.3rem}
.hero h1 .g{background:linear-gradient(120deg,var(--cyan) 0%,var(--mint) 60%,#88ffee 100%);-webkit-background-clip:text;-webkit-text-fill-color:transparent;background-clip:text}
.hero-sub{font-family:'Playfair Display',Georgia,serif;font-style:italic;font-size:1rem;color:var(--text-dim);margin-bottom:0.8rem}
.hero-desc{font-size:0.92rem;color:var(--text-dim);max-width:620px;margin:0 auto;line-height:1.7}
/* Section Labels */
.section-label{font-family:'DM Mono',monospace;font-size:0.6rem;letter-spacing:0.2em;text-transform:uppercase;color:var(--cyan);margin-bottom:1.2rem;padding-left:0.2rem}
/* Cards */
.card{background:var(--card-bg);border:1px solid var(--card-border);border-radius:16px;padding:2rem 2.2rem;backdrop-filter:blur(18px);margin-bottom:2.5rem;transition:all 0.3s;box-shadow:0 8px 32px rgba(0,0,0,0.04)}
.card-title{font-size:1.15rem;font-weight:700;color:var(--text-bright);margin-bottom:1.2rem;display:flex;align-items:center;gap:0.5rem}
.card-subtitle{font-size:0.85rem;font-weight:600;color:var(--cyan);margin-bottom:0.6rem;text-transform:uppercase;letter-spacing:0.05em;font-family:'DM Mono',monospace}
.card p, .card li{font-size:0.92rem;line-height:1.7;color:var(--text)}
.card ul, .card ol{padding-left:1.4rem;margin-bottom:1rem}
.card li{margin-bottom:0.3rem}
/* Formula Display */
.formula-box{background:linear-gradient(135deg,var(--cyan-dim),var(--mint-dim));border:1px solid rgba(0,229,255,0.25);border-radius:14px;padding:2rem;text-align:center;margin:1.5rem 0}
.formula-main{font-size:clamp(1.4rem,4vw,2.2rem);font-weight:800;color:var(--text-bright);font-family:'DM Mono',monospace;letter-spacing:-0.02em;margin-bottom:0.5rem}
.formula-alt{font-size:clamp(1rem,2.5vw,1.4rem);font-weight:600;color:var(--cyan);font-family:'DM Mono',monospace;margin-top:0.5rem}
.formula-label{font-size:0.75rem;color:var(--text-dim);font-family:'DM Mono',monospace;text-transform:uppercase;letter-spacing:0.12em;margin-top:0.8rem}
/* Variable Cards */
.var-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(200px,1fr));gap:1rem;margin:1.2rem 0}
.var-card{background:var(--glass);border:1px solid var(--glass-border);border-radius:12px;padding:1rem 1.2rem;text-align:center;transition:all 0.2s}
.var-card:hover{border-color:var(--cyan);transform:translateY(-2px)}
.var-symbol{font-family:'DM Mono',monospace;font-size:1.5rem;font-weight:700;margin-bottom:0.3rem}
.var-name{font-size:0.82rem;font-weight:600;color:var(--text-bright);margin-bottom:0.2rem}
.var-desc{font-size:0.72rem;color:var(--text-dim);line-height:1.5}
.vc1 .var-symbol{color:var(--cyan)}
.vc2 .var-symbol{color:var(--mint)}
.vc3 .var-symbol{color:var(--amber)}
.vc4 .var-symbol{color:var(--purple)}
/* Step List */
.step-list{list-style:none;counter-reset:step-counter}
.step-item{position:relative;padding-left:3rem;margin-bottom:1.2rem;font-size:0.92rem;color:var(--text);line-height:1.6}
.step-item::before{content:counter(step-counter);counter-increment:step-counter;position:absolute;left:0;top:-1px;width:24px;height:24px;border-radius:50%;background:var(--cyan-dim);color:var(--cyan);font-family:'DM Mono',monospace;font-size:0.75rem;font-weight:600;display:flex;align-items:center;justify-content:center;border:1px solid rgba(0,229,255,0.2)}
.step-item:last-child{margin-bottom:0}
.highlight{color:var(--cyan);font-family:'DM Mono',monospace;font-size:0.85rem;padding:0.15rem 0.4rem;background:var(--cyan-dim);border-radius:4px;border:1px solid rgba(0,229,255,0.15)}
/* Alerts */
.alert{padding:1rem 1.2rem;border-radius:10px;margin:1rem 0;font-size:0.85rem;line-height:1.65}
.alert-info{background:var(--cyan-dim);border:1px solid rgba(0,229,255,0.16);color:var(--text)}
.alert-warn{background:var(--amber-dim);border:1px solid rgba(255,183,0,0.2);color:var(--text)}
.alert-danger{background:var(--red-dim);border:1px solid rgba(255,77,109,0.2);color:var(--text)}
.alert-title{font-weight:700;margin-bottom:0.3rem;font-size:0.78rem;text-transform:uppercase;letter-spacing:0.05em;display:flex;align-items:center;gap:0.4rem}
.alert-info .alert-title{color:var(--cyan)}
.alert-warn .alert-title{color:var(--amber)}
.alert-danger .alert-title{color:var(--red)}
/* Examples */
.example-box{background:var(--glass);border:1px solid var(--glass-border);border-radius:12px;padding:1.5rem;margin:1.2rem 0}
.example-title{font-size:0.75rem;font-weight:700;text-transform:uppercase;letter-spacing:0.12em;color:var(--mint);margin-bottom:0.8rem;font-family:'DM Mono',monospace}
.example-given{font-size:0.88rem;color:var(--text);margin-bottom:0.8rem;line-height:1.6}
.example-calc{font-family:'DM Mono',monospace;font-size:0.85rem;color:var(--text-bright);background:var(--card-bg);border:1px solid var(--card-border);border-radius:8px;padding:1rem;line-height:1.8;overflow-x:auto}
.example-answer{margin-top:0.8rem;font-weight:700;color:var(--cyan);font-size:0.92rem}
/* Calculator */
.calc-grid{display:grid;grid-template-columns:1fr 1fr;gap:1rem;margin:1.2rem 0}
@media(max-width:500px){.calc-grid{grid-template-columns:1fr}}
.calc-group{display:flex;flex-direction:column;gap:0.3rem}
.calc-label{font-family:'DM Mono',monospace;font-size:0.7rem;letter-spacing:0.08em;color:var(--text-dim);text-transform:uppercase}
.calc-input{font-family:'DM Mono',monospace;font-size:1rem;padding:0.7rem 1rem;border-radius:10px;border:1px solid var(--input-border);background:var(--input-bg);color:var(--text-bright);outline:none;transition:all 0.2s;-moz-appearance:textfield;appearance:textfield}
.calc-input::-webkit-outer-spin-button,.calc-input::-webkit-inner-spin-button{-webkit-appearance:none;appearance:none;margin:0}
.calc-input:focus{border-color:var(--cyan);box-shadow:0 0 0 3px var(--cyan-dim)}
.calc-select{font-family:'DM Mono',monospace;font-size:0.85rem;padding:0.7rem 1rem;border-radius:10px;border:1px solid var(--input-border);background:var(--input-bg);color:var(--text-bright);outline:none;transition:all 0.2s;cursor:pointer}
.calc-select:focus{border-color:var(--cyan);box-shadow:0 0 0 3px var(--cyan-dim)}
.calc-result{background:linear-gradient(135deg,var(--mint-dim),var(--cyan-dim));border:1px solid rgba(0,255,179,0.25);border-radius:14px;padding:1.5rem;text-align:center;margin-top:1rem;animation:fadeIn 0.3s ease}
@keyframes fadeIn{from{opacity:0;transform:scale(0.98)}to{opacity:1;transform:scale(1)}}
.calc-result-label{font-family:'DM Mono',monospace;font-size:0.65rem;letter-spacing:0.15em;text-transform:uppercase;color:var(--text-dim);margin-bottom:0.3rem}
.calc-result-value{font-family:'DM Mono',monospace;font-size:2rem;font-weight:800;color:var(--text-bright)}
.calc-result-unit{font-size:0.9rem;color:var(--mint);margin-left:0.3rem}
.calc-btn-row{display:flex;gap:0.8rem;margin-top:1rem;flex-wrap:wrap}
.calc-btn{flex:1;min-width:120px;font-family:'DM Mono',monospace;font-size:0.75rem;letter-spacing:0.06em;padding:0.65rem 1rem;border-radius:100px;border:1px solid var(--cyan);background:var(--cyan-dim);color:var(--cyan);cursor:pointer;transition:all 0.2s;font-weight:600}
.calc-btn:hover{background:var(--cyan);color:var(--bg)}
.calc-btn.active{background:var(--cyan);color:var(--bg)}
/* Table */
table{width:100%;border-collapse:collapse;margin:1rem 0;font-size:0.85rem}
th,td{padding:0.75rem 1rem;text-align:left;border-bottom:1px solid var(--glass-border)}
th{font-weight:600;color:var(--text-bright);background:var(--glass);font-family:'DM Mono',monospace;font-size:0.75rem;letter-spacing:0.05em;text-transform:uppercase}
td{color:var(--text)}
td code{font-family:'DM Mono',monospace;font-size:0.82rem;color:var(--cyan);background:var(--cyan-dim);padding:0.1rem 0.35rem;border-radius:4px}
/* Derivation */
.derivation{font-family:'DM Mono',monospace;font-size:0.9rem;line-height:2;color:var(--text-bright);text-align:center;margin:1rem 0}
.derivation .step{margin-bottom:0.5rem}
.derivation .arrow{color:var(--cyan);font-size:1.2rem}
/* Quiz */
.quiz-box{background:var(--glass);border:1px solid var(--glass-border);border-radius:12px;padding:1.5rem;margin:1.2rem 0}
.qz-num{font-family:'DM Mono',monospace;font-size:0.75rem;letter-spacing:0.12em;color:var(--mint);text-transform:uppercase;margin-bottom:0.8rem;font-weight:700}
.qz-q{font-size:0.92rem;color:var(--text-bright);margin-bottom:1.2rem;line-height:1.6}
.qz-opts{display:flex;flex-direction:column;gap:0.6rem;margin-bottom:1.2rem}
.qz-opt{text-align:left;font-family:'Inter',sans-serif;font-size:0.88rem;padding:0.8rem 1rem;border:1px solid var(--card-border);background:var(--card-bg);color:var(--text);border-radius:8px;cursor:pointer;transition:all 0.2s}
.qz-opt:hover{border-color:var(--cyan);background:var(--cyan-dim)}
.qz-opt.selected{border-color:var(--cyan);background:var(--cyan-dim);color:var(--text-bright);font-weight:600}
.qz-opt.correct{border-color:var(--mint);background:var(--mint-dim);color:var(--mint);font-weight:700}
.qz-opt.wrong{border-color:var(--red);background:var(--red-dim);color:var(--red);opacity:0.6}
.qz-feedback{display:none;padding:1rem;border-radius:8px;font-size:0.85rem;line-height:1.5;margin-top:1rem;animation:fadeIn 0.3s ease}
.qz-feedback.show{display:block}
.qz-feedback.success{background:linear-gradient(135deg,rgba(0,255,179,0.1),var(--mint-dim));border:1px solid rgba(0,255,179,0.2)}
.qz-feedback.error{background:linear-gradient(135deg,rgba(255,77,109,0.1),var(--red-dim));border:1px solid rgba(255,77,109,0.2)}
.qz-action{font-family:'DM Mono',monospace;font-size:0.75rem;padding:0.6rem 1.2rem;border-radius:100px;border:none;background:var(--cyan);color:var(--bg);font-weight:700;cursor:pointer;transition:all 0.2s;letter-spacing:0.05em}
.qz-action:hover{filter:brightness(1.1);transform:translateY(-1px)}
.qz-action:disabled{opacity:0.5;cursor:not-allowed;transform:none}
/* Nav Card */
.nav-card{display:flex;align-items:center;justify-content:space-between;background:var(--card-bg);border:1px solid var(--card-border);border-radius:12px;padding:1.2rem 1.5rem;text-decoration:none;color:inherit;transition:all 0.3s;margin-top:1.5rem}
.nav-card:hover{background:var(--card-hover);border-color:var(--mint);transform:translateX(5px)}
.nav-label{font-family:'DM Mono',monospace;font-size:0.6rem;letter-spacing:0.15em;text-transform:uppercase;color:var(--text-dim)}
.nav-title{font-size:0.95rem;font-weight:700;color:var(--text-bright)}
/* Footer */
.footer{text-align:center;font-family:'DM Mono',monospace;font-size:0.58rem;letter-spacing:0.14em;color:var(--text-dim);text-transform:uppercase;margin-top:3rem}
/* Reveal */
.reveal{opacity:0;transform:translateY(25px);transition:opacity 0.6s ease, transform 0.6s ease}
.reveal.visible{opacity:1;transform:translateY(0)}
/* Print */
@media print{
  .bg-canvas,.grid-overlay,.topbar,.calc-btn-row{display:none!important}
  .main{padding:0}
  .card{border:1px solid #ccc;box-shadow:none;backdrop-filter:none;break-inside:avoid}
  body{background:white;color:#111}
  .hero h1 .g{-webkit-text-fill-color:#0080aa}
  .formula-main,.formula-alt{color:#0080aa!important;-webkit-text-fill-color:#0080aa}
  h1,h2,.card-title{color:#0a2040!important}
  @page{margin:1.5cm;size:A4}
}
@media(max-width:600px){
  .hero h1{font-size:1.8rem}
  .card{padding:1.4rem}
  .step-item{padding-left:2.5rem}
  .formula-box{padding:1.2rem}
  .var-grid{grid-template-columns:1fr 1fr}
}