/* ===== RESET & BASE ===== */
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
:root{
  --bg:linear-gradient(135deg,#0a0e1a 0%,#111827 40%,#0f172a 100%);
  --surface:rgba(255,255,255,0.04);
  --surface-hover:rgba(255,255,255,0.08);
  --border:rgba(255,255,255,0.08);
  --border-glow:rgba(96,165,250,0.3);
  --text:#e2e8f0;
  --text-dim:#94a3b8;
  --text-bright:#f8fafc;
  --accent:#60a5fa;
  --accent2:#818cf8;
  --accent3:#a78bfa;
  --gold:#fbbf24;
  --radius:16px;
  --radius-sm:10px;
  --shadow:0 8px 32px rgba(0,0,0,0.4);
}
html{scroll-behavior:smooth;font-size:16px}
body{font-family:'Inter',sans-serif;background:var(--bg);color:var(--text);min-height:100vh;overflow-x:hidden;line-height:1.6}
a{color:inherit;text-decoration:none}

/* ===== AMBIENT BG ===== */
.ambient-bg{position:fixed;inset:0;z-index:0;pointer-events:none;overflow:hidden}
.ambient-bg::before{content:'';position:absolute;width:600px;height:600px;background:radial-gradient(circle,rgba(96,165,250,0.08),transparent 70%);top:-100px;right:-100px;animation:ambFloat 20s ease-in-out infinite}
.ambient-bg::after{content:'';position:absolute;width:500px;height:500px;background:radial-gradient(circle,rgba(167,139,250,0.06),transparent 70%);bottom:-100px;left:-100px;animation:ambFloat 25s ease-in-out infinite reverse}
@keyframes ambFloat{0%,100%{transform:translate(0,0)}50%{transform:translate(40px,30px)}}

/* ===== HEADER ===== */
.header{position:fixed;top:0;left:0;right:0;z-index:100;padding:1rem 2rem;backdrop-filter:blur(20px);background:rgba(10,14,26,0.7);border-bottom:1px solid var(--border);transition:all .3s}
.header-inner{max-width:1200px;margin:0 auto;display:flex;justify-content:space-between;align-items:center}
.logo{display:flex;align-items:center;gap:.6rem}
.logo-icon{width:36px;height:36px}
.logo-icon svg{width:100%;height:100%}
.logo-text{font-family:'Outfit',sans-serif;font-weight:700;font-size:1.25rem;background:linear-gradient(135deg,var(--accent),var(--accent3));-webkit-background-clip:text;-webkit-text-fill-color:transparent}
.nav{display:flex;gap:2rem}
.nav-link{font-size:.875rem;font-weight:500;color:var(--text-dim);transition:color .3s;position:relative}
.nav-link:hover,.nav-link.active{color:var(--accent)}
.nav-link.active::after{content:'';position:absolute;bottom:-4px;left:0;right:0;height:2px;background:var(--accent);border-radius:2px}

/* ===== HERO ===== */
.hero{position:relative;z-index:1;min-height:100vh;display:flex;align-items:center;padding:8rem 2rem 4rem;max-width:1200px;margin:0 auto;gap:4rem}
.hero-content{flex:1}
.hero-badge{display:inline-block;padding:.4rem 1rem;border-radius:100px;background:rgba(96,165,250,0.1);border:1px solid rgba(96,165,250,0.2);color:var(--accent);font-size:.8rem;font-weight:600;letter-spacing:.05em;margin-bottom:1.5rem}
.hero-title{font-family:'Outfit',sans-serif;font-size:clamp(2.5rem,5vw,4rem);font-weight:800;line-height:1.1;color:var(--text-bright)}
.hero-accent{background:linear-gradient(135deg,var(--accent),var(--accent3));-webkit-background-clip:text;-webkit-text-fill-color:transparent;font-style:italic}
.hero-subtitle-line{display:block;background:linear-gradient(135deg,var(--gold),#f59e0b);-webkit-background-clip:text;-webkit-text-fill-color:transparent}
.hero-description{margin-top:1.5rem;font-size:1.1rem;color:var(--text-dim);max-width:480px;line-height:1.8}
.hero-cta{display:inline-flex;align-items:center;gap:.6rem;margin-top:2rem;padding:.9rem 2rem;background:linear-gradient(135deg,var(--accent),var(--accent2));border-radius:100px;font-weight:600;color:#fff;transition:transform .3s,box-shadow .3s;box-shadow:0 4px 20px rgba(96,165,250,0.3)}
.hero-cta:hover{transform:translateY(-2px);box-shadow:0 8px 30px rgba(96,165,250,0.5)}

/* Hero Diagram */
.hero-visual{flex:1;display:flex;justify-content:center}
.hero-diagram{display:flex;align-items:center;gap:2rem}
.gallon-container{width:100px;height:140px;border:2px solid var(--border-glow);border-radius:12px 12px 16px 16px;position:relative;overflow:hidden;background:rgba(96,165,250,0.05)}
.gallon-liquid{position:absolute;bottom:0;left:0;right:0;height:70%;background:linear-gradient(180deg,rgba(96,165,250,0.3),rgba(96,165,250,0.6));border-radius:0 0 14px 14px;animation:liquidPulse 3s ease-in-out infinite}
@keyframes liquidPulse{0%,100%{height:70%}50%{height:75%}}
.gallon-label{position:absolute;top:50%;left:50%;transform:translate(-50%,-50%);font-weight:700;font-size:1.2rem;color:var(--accent);text-shadow:0 0 20px rgba(96,165,250,0.5)}
.diagram-arrow{display:flex;flex-direction:column;align-items:center;gap:.5rem}
.arrow-line{width:60px;height:2px;background:linear-gradient(90deg,var(--accent),var(--accent3));position:relative}
.arrow-particles span{display:block;width:6px;height:6px;border-radius:50%;background:var(--accent);animation:particleFlow 2s infinite;opacity:0}
.arrow-particles span:nth-child(2){animation-delay:.6s}
.arrow-particles span:nth-child(3){animation-delay:1.2s}
@keyframes particleFlow{0%{opacity:0;transform:translateX(-20px)}50%{opacity:1}100%{opacity:0;transform:translateX(20px)}}
.scale-base{display:flex;flex-direction:column;align-items:center}
.scale-plate{width:100px;height:100px;border:2px solid rgba(251,191,36,0.3);border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:2.5rem;background:rgba(251,191,36,0.05)}
.scale-label{margin-top:.5rem;font-weight:700;font-size:1.2rem;color:var(--gold)}

/* ===== SECTIONS COMMON ===== */
.calculator-section,.how-section,.chart-section{position:relative;z-index:1;padding:6rem 2rem;max-width:1200px;margin:0 auto}
.section-header{text-align:center;margin-bottom:3rem}
.section-badge{display:inline-block;padding:.35rem .9rem;border-radius:100px;background:rgba(96,165,250,0.1);border:1px solid rgba(96,165,250,0.15);color:var(--accent);font-size:.75rem;font-weight:600;letter-spacing:.08em;text-transform:uppercase;margin-bottom:1rem}
.section-title{font-family:'Outfit',sans-serif;font-size:clamp(1.8rem,3vw,2.5rem);font-weight:700;color:var(--text-bright)}
.section-desc{margin-top:.75rem;color:var(--text-dim);max-width:560px;margin-left:auto;margin-right:auto}

/* ===== CALCULATOR ===== */
.calculator-layout{display:grid;grid-template-columns:1fr 1.4fr 1fr;gap:1.5rem;align-items:start}
.calc-panel{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:1.8rem;backdrop-filter:blur(10px);transition:border-color .3s}
.calc-panel:hover{border-color:var(--border-glow)}
.panel-header{display:flex;align-items:center;gap:.75rem;margin-bottom:1.5rem}
.panel-icon{width:40px;height:40px;border-radius:var(--radius-sm);display:flex;align-items:center;justify-content:center}
.input-icon{background:rgba(96,165,250,0.15);color:var(--accent)}
.visual-icon{background:rgba(167,139,250,0.15);color:var(--accent3)}
.output-icon{background:rgba(251,191,36,0.15);color:var(--gold)}
.panel-title{font-family:'Outfit',sans-serif;font-weight:600;font-size:1.1rem}

/* Form */
.form-group{margin-bottom:1.2rem}
.form-label{display:block;font-size:.8rem;font-weight:600;color:var(--text-dim);margin-bottom:.5rem;letter-spacing:.03em;text-transform:uppercase}
.select-wrapper{position:relative}
.form-select,.form-input{width:100%;padding:.75rem 1rem;background:rgba(255,255,255,0.05);border:1px solid var(--border);border-radius:var(--radius-sm);color:var(--text-bright);font-size:.95rem;font-family:'Inter',sans-serif;transition:border-color .3s,box-shadow .3s;outline:none;-webkit-appearance:none;appearance:none}
.form-select:focus,.form-input:focus{border-color:var(--accent);box-shadow:0 0 0 3px rgba(96,165,250,0.15)}
.form-select option{background:#1e293b;color:var(--text)}
.select-arrow{position:absolute;right:12px;top:50%;transform:translateY(-50%);color:var(--text-dim);pointer-events:none}
.convert-btn{width:100%;padding:.85rem;background:linear-gradient(135deg,var(--accent),var(--accent2));border:none;border-radius:var(--radius-sm);color:#fff;font-family:'Inter',sans-serif;font-weight:600;font-size:1rem;cursor:pointer;display:flex;align-items:center;justify-content:center;gap:.5rem;transition:transform .2s,box-shadow .2s;box-shadow:0 4px 15px rgba(96,165,250,0.3)}
.convert-btn:hover{transform:translateY(-2px);box-shadow:0 6px 25px rgba(96,165,250,0.4)}
.convert-btn:active{transform:translateY(0)}

/* ===== VISUAL DIAGRAM ===== */
.viz-stage{display:flex;align-items:center;justify-content:center;gap:1rem;padding:1.5rem .5rem;min-height:200px}
.viz-gallon-wrap,.viz-scale-wrap{flex:0 0 auto}
.viz-gallon{display:flex;flex-direction:column;align-items:center}
.viz-gallon-neck{width:30px;height:14px;border:2px solid var(--border-glow);border-bottom:none;border-radius:6px 6px 0 0;background:rgba(96,165,250,0.05)}
.viz-gallon-body{width:80px;height:110px;border:2px solid var(--border-glow);border-radius:4px 4px 12px 12px;position:relative;overflow:hidden;background:rgba(96,165,250,0.03)}
.viz-liquid{position:absolute;bottom:0;left:0;right:0;height:70%;background:linear-gradient(180deg,rgba(96,165,250,0.4),rgba(59,130,246,0.7));transition:height .8s cubic-bezier(.4,0,.2,1),background .5s}
.viz-wave{position:absolute;top:-4px;left:-10%;width:120%;height:10px;background:radial-gradient(ellipse at center,rgba(255,255,255,0.2),transparent);border-radius:50%;animation:waveMove 2s ease-in-out infinite}
@keyframes waveMove{0%,100%{transform:translateX(-5%)}50%{transform:translateX(5%)}}
.viz-measure-lines{position:absolute;right:4px;top:10%;bottom:10%;display:flex;flex-direction:column;justify-content:space-between}
.viz-measure-lines span{width:10px;height:1px;background:rgba(255,255,255,0.15)}
.viz-gallon-value{margin-top:.5rem;font-size:.8rem;font-weight:600;color:var(--accent)}

/* Flow */
.viz-flow{display:flex;flex-direction:column;align-items:center;gap:.4rem;padding:0 .3rem}
.viz-flow-line{height:2px;width:40px;background:linear-gradient(90deg,transparent,var(--accent),transparent);position:relative}
.viz-flow-dot{position:absolute;width:5px;height:5px;border-radius:50%;background:var(--accent);top:-1.5px;animation:dotFlow 2.5s infinite linear;opacity:0}
.viz-flow-dot:nth-child(2){animation-delay:.8s}
.viz-flow-dot:nth-child(3){animation-delay:1.6s}
@keyframes dotFlow{0%{left:0;opacity:0}20%{opacity:1}80%{opacity:1}100%{left:100%;opacity:0}}
.viz-multiply{display:flex;align-items:center;gap:.3rem;padding:.4rem .7rem;background:rgba(167,139,250,0.12);border:1px solid rgba(167,139,250,0.2);border-radius:100px}
.viz-multiply-sign{color:var(--accent3);font-weight:700;font-size:1rem}
.viz-density-val{font-size:.85rem;font-weight:700;color:var(--text-bright)}

/* Scale */
.viz-scale{display:flex;flex-direction:column;align-items:center}
.viz-scale-display{font-family:'Outfit',sans-serif;font-size:1.8rem;font-weight:800;color:var(--gold);text-shadow:0 0 20px rgba(251,191,36,0.3);transition:all .5s}
.viz-scale-unit{font-size:.75rem;color:var(--text-dim);font-weight:600;letter-spacing:.05em;text-transform:uppercase}
.viz-scale-platform{width:70px;height:8px;background:linear-gradient(90deg,var(--border),rgba(251,191,36,0.3),var(--border));border-radius:4px;margin-top:.5rem;position:relative}
.viz-scale-needle{position:absolute;width:3px;height:16px;background:var(--gold);border-radius:2px;top:-4px;left:50%;transform:translateX(-50%);transition:left .6s cubic-bezier(.4,0,.2,1)}
.viz-scale-base{width:40px;height:6px;background:var(--border);border-radius:0 0 4px 4px;margin:0 auto}

/* Formula */
.viz-formula{display:flex;align-items:center;justify-content:center;gap:.5rem;flex-wrap:wrap;margin-top:1.2rem;padding:.8rem;background:rgba(255,255,255,0.03);border-radius:var(--radius-sm);border:1px solid var(--border)}
.formula-part{padding:.3rem .6rem;border-radius:6px;font-weight:600;font-size:.85rem}
.gallons-part{background:rgba(96,165,250,0.12);color:var(--accent)}
.density-part{background:rgba(167,139,250,0.12);color:var(--accent3)}
.result-part{background:rgba(251,191,36,0.12);color:var(--gold)}
.formula-op{color:var(--text-dim);font-weight:700}

/* ===== RESULT ===== */
.result-display{text-align:center;padding:2rem 0;border-bottom:1px solid var(--border);margin-bottom:1.2rem}
.result-value{font-family:'Outfit',sans-serif;font-size:3rem;font-weight:800;background:linear-gradient(135deg,var(--gold),#f59e0b);-webkit-background-clip:text;-webkit-text-fill-color:transparent;transition:all .4s}
.result-unit{font-size:.85rem;color:var(--text-dim);font-weight:500;margin-top:.25rem}
.result-details{display:flex;flex-direction:column;gap:.6rem}
.detail-row{display:flex;justify-content:space-between;align-items:center;padding:.5rem .6rem;border-radius:8px;transition:background .2s}
.detail-row:hover{background:rgba(255,255,255,0.03)}
.detail-label{font-size:.8rem;color:var(--text-dim)}
.detail-value{font-size:.85rem;font-weight:600;color:var(--text-bright)}

/* ===== HOW IT WORKS ===== */
.steps-grid{display:grid;grid-template-columns:repeat(4,1fr);gap:1.5rem}
.step-card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:2rem 1.5rem;text-align:center;transition:transform .3s,border-color .3s,box-shadow .3s;position:relative;overflow:hidden}
.step-card::before{content:'';position:absolute;top:0;left:0;right:0;height:3px;background:linear-gradient(90deg,var(--accent),var(--accent3));opacity:0;transition:opacity .3s}
.step-card:hover{transform:translateY(-4px);border-color:var(--border-glow);box-shadow:var(--shadow)}
.step-card:hover::before{opacity:1}
.step-number{font-family:'Outfit',sans-serif;font-size:2.5rem;font-weight:800;background:linear-gradient(135deg,rgba(96,165,250,0.15),rgba(167,139,250,0.15));-webkit-background-clip:text;-webkit-text-fill-color:transparent;margin-bottom:.5rem}
.step-icon{margin-bottom:1rem;color:var(--accent)}
.step-icon svg{width:48px;height:48px}
.step-title{font-family:'Outfit',sans-serif;font-weight:600;font-size:1.05rem;margin-bottom:.5rem;color:var(--text-bright)}
.step-desc{font-size:.85rem;color:var(--text-dim);line-height:1.6}

/* ===== CHART ===== */
.chart-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:1.5rem}
.chart-card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:1.8rem;text-align:center;transition:transform .3s,border-color .3s;cursor:pointer}
.chart-card:hover{transform:translateY(-3px);border-color:var(--border-glow)}
.chart-liquid-icon{font-size:2.5rem;margin-bottom:.75rem}
.chart-liquid-name{font-family:'Outfit',sans-serif;font-weight:600;font-size:1rem;margin-bottom:.5rem;color:var(--text-bright)}
.chart-liquid-weight{font-size:1.4rem;font-weight:700;color:var(--accent);margin-bottom:1rem}
.chart-liquid-weight small{font-size:.7rem;font-weight:500;color:var(--text-dim)}
.chart-bar{height:6px;background:rgba(255,255,255,0.05);border-radius:3px;overflow:hidden}
.chart-bar-fill{height:100%;width:var(--fill);background:linear-gradient(90deg,var(--accent),var(--accent2));border-radius:3px;transition:width 1s cubic-bezier(.4,0,.2,1)}

/* ===== FOOTER ===== */
.footer{position:relative;z-index:1;border-top:1px solid var(--border);padding:3rem 2rem;margin-top:4rem}
.footer-inner{max-width:1200px;margin:0 auto;display:flex;justify-content:space-between;align-items:center}
.footer-tagline{color:var(--text-dim);font-size:.85rem;margin-top:.5rem}
.footer-copy{font-size:.8rem;color:var(--text-dim)}

/* ===== ANIMATIONS ===== */
.calc-panel,.step-card,.chart-card{opacity:0;transform:translateY(30px);animation:fadeUp .6s ease forwards}
.calc-panel:nth-child(2){animation-delay:.15s}
.calc-panel:nth-child(3){animation-delay:.3s}
.step-card[data-step="2"]{animation-delay:.15s}
.step-card[data-step="3"]{animation-delay:.3s}
.step-card[data-step="4"]{animation-delay:.45s}
.chart-card:nth-child(2){animation-delay:.1s}
.chart-card:nth-child(3){animation-delay:.2s}
.chart-card:nth-child(4){animation-delay:.3s}
.chart-card:nth-child(5){animation-delay:.4s}
.chart-card:nth-child(6){animation-delay:.5s}
@keyframes fadeUp{to{opacity:1;transform:translateY(0)}}

/* Glow effect on result change */
.result-glow{animation:glowPulse .6s ease}
@keyframes glowPulse{0%{filter:brightness(1)}50%{filter:brightness(1.5) drop-shadow(0 0 20px rgba(251,191,36,0.5))}100%{filter:brightness(1)}}

/* ===== RESPONSIVE ===== */
@media(max-width:1024px){
  .calculator-layout{grid-template-columns:1fr}
  .hero{flex-direction:column;text-align:center;min-height:auto;padding-top:7rem}
  .hero-description{margin-left:auto;margin-right:auto}
  .steps-grid{grid-template-columns:repeat(2,1fr)}
}
@media(max-width:768px){
  .header{padding:.75rem 1rem}
  .nav{gap:1rem}
  .nav-link{font-size:.8rem}
  .hero-diagram{transform:scale(.85)}
  .chart-grid{grid-template-columns:1fr 1fr}
  .viz-stage{flex-direction:column;gap:1.5rem}
  .viz-flow{flex-direction:row}
  .viz-flow-line{width:2px;height:30px}
}
@media(max-width:480px){
  .steps-grid{grid-template-columns:1fr}
  .chart-grid{grid-template-columns:1fr}
  .hero-title{font-size:2rem}
  .nav{gap:.6rem}
}