/* ===== CSS Variables ===== */
:root {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --bg-card: #ffffff;
  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --text-primary: #1e293b;
  --text-secondary: #475569;
  --text-muted: #94a3b8;
  --border: #e2e8f0;
  --radius: 8px;
  --shadow: 0 1px 3px rgba(0,0,0,.06), 0 1px 2px rgba(0,0,0,.04);
  --shadow-md: 0 4px 6px rgba(0,0,0,.06), 0 2px 4px rgba(0,0,0,.04);
  --header-h: 64px;
  --max-w: 1000px;
}

/* ===== Dark Mode ===== */
[data-theme="dark"] {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-card: #1e293b;
  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --border: #334155;
  --shadow: 0 1px 3px rgba(0,0,0,.3), 0 1px 2px rgba(0,0,0,.2);
  --shadow-md: 0 4px 6px rgba(0,0,0,.3), 0 2px 4px rgba(0,0,0,.2);
}
[data-theme="dark"] .hero{background:linear-gradient(135deg,#1e293b 0%,#0f172a 100%)}
[data-theme="dark"] .result-box{background:#162032;border-color:#334155}
[data-theme="dark"] .info-box{background:#162032;border-left-color:var(--accent)}
[data-theme="dark"] .comparison-table th{background:#162032}
[data-theme="dark"] .comparison-table tr:hover td{background:#162032}
[data-theme="dark"] .faq-section details[open] summary{background:#162032}
[data-theme="dark"] .faq-q.open{background:#162032}
[data-theme="dark"] .ad-spot{background:#1e293b;border-color:#334155}

/* ===== Reset ===== */
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth;-webkit-text-size-adjust:100%}
body{font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,'Helvetica Neue',Arial,sans-serif;background:var(--bg-primary);color:var(--text-primary);line-height:1.6;min-height:100vh;display:flex;flex-direction:column}
img{max-width:100%;display:block}
a{color:var(--accent);text-decoration:none}
a:hover{color:var(--accent-hover)}
ul,ol{list-style:none}
input,select,button,textarea{font:inherit;color:inherit}

/* ===== Container ===== */
.container{width:100%;max-width:var(--max-w);margin:0 auto;padding:0 20px}

/* ===== Header ===== */
.site-header{background:var(--bg-secondary);height:var(--header-h);border-bottom:1px solid var(--border);box-shadow:var(--shadow);position:sticky;top:0;z-index:100}
.site-header .container{display:flex;align-items:center;justify-content:space-between;height:100%}
.logo{font-size:1.35rem;font-weight:700;color:var(--text-primary);display:flex;align-items:center;gap:2px}
.logo span{color:var(--accent)}
.nav-links{display:flex;gap:6px}
.nav-links a{padding:8px 14px;border-radius:var(--radius);font-size:.9rem;font-weight:500;color:var(--text-secondary);transition:background .2s,color .2s}
.nav-links a:hover,.nav-links a.active{background:var(--accent);color:#fff}
nav{display:flex;align-items:center;gap:4px}
.menu-toggle{display:none;background:none;border:none;cursor:pointer;padding:6px}
.menu-toggle span{display:block;width:22px;height:2px;background:var(--text-primary);margin:5px 0;border-radius:2px;transition:transform .3s,opacity .3s}
.dark-mode-btn{background:none;border:none;font-size:1.3rem;cursor:pointer;padding:6px;color:var(--text-primary);transition:color .2s;line-height:1}
.dark-mode-btn:hover{color:var(--accent)}

/* ===== Hero ===== */
.hero{background:linear-gradient(135deg,#eff6ff 0%,#f8fafc 100%);padding:48px 0 40px;text-align:center}
.hero h1{font-size:2rem;font-weight:700;margin-bottom:12px;color:var(--text-primary)}
.hero p{font-size:1.1rem;color:var(--text-secondary);max-width:560px;margin:0 auto}
.hero-illustration{width:160px;height:160px;margin:28px auto 0;display:block}
.hero-illustration svg{width:160px;height:160px;display:block}

/* ===== Breadcrumb ===== */
.breadcrumb{padding:14px 0;font-size:.85rem;color:var(--text-muted)}
.breadcrumb a{color:var(--text-secondary)}
.breadcrumb a:hover{color:var(--accent)}
.breadcrumb span{margin:0 6px}

/* ===== Card Grid ===== */
.card-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:20px;padding:32px 0}
.card{background:var(--bg-card);border:1px solid var(--border);border-radius:var(--radius);padding:28px 24px;transition:box-shadow .2s,transform .15s;display:flex;flex-direction:column;gap:10px}
.card:hover{box-shadow:var(--shadow-md);transform:translateY(-2px)}
.card .card-icon{font-size:2rem;margin-bottom:4px}
.card h3{font-size:1.1rem;font-weight:600}
.card p{font-size:.9rem;color:var(--text-secondary);flex:1}
.card .card-link{display:inline-flex;align-items:center;gap:4px;font-size:.9rem;font-weight:600;color:var(--accent);margin-top:6px}
.card .card-link:hover{color:var(--accent-hover)}

/* ===== Section Heading ===== */
.section-heading{font-size:1.35rem;font-weight:700;margin:40px 0 8px;padding-bottom:8px;border-bottom:2px solid var(--accent);display:inline-block}

/* ===== Buttons ===== */
.btn{display:inline-flex;align-items:center;justify-content:center;gap:6px;padding:10px 22px;border-radius:var(--radius);font-weight:600;font-size:.95rem;border:1px solid var(--border);background:var(--bg-secondary);color:var(--text-primary);cursor:pointer;transition:background .2s,color .2s,border-color .2s}
.btn:hover{border-color:var(--accent);color:var(--accent)}
.btn-primary{background:var(--accent);color:#fff;border-color:var(--accent)}
.btn-primary:hover{background:var(--accent-hover);border-color:var(--accent-hover)}
.btn-sm{padding:7px 16px;font-size:.85rem}

/* ===== Tool Container (Calculator Pages) ===== */
.tool-container{background:var(--bg-card);border:1px solid var(--border);border-radius:var(--radius);padding:32px;margin:24px 0;box-shadow:var(--shadow)}

/* ===== Form ===== */
.form-group{margin-bottom:18px}
.form-group label{display:block;font-size:.9rem;font-weight:600;margin-bottom:6px;color:var(--text-primary)}
.form-group input,.form-group select{width:100%;padding:10px 14px;border:1px solid var(--border);border-radius:var(--radius);background:var(--bg-secondary);font-size:.95rem;transition:border-color .2s}
.form-group input:focus,.form-group select:focus{outline:none;border-color:var(--accent);box-shadow:0 0 0 3px rgba(37,99,235,.1)}
.form-row{display:grid;grid-template-columns:1fr 1fr;gap:16px}
.form-row-3{display:grid;grid-template-columns:1fr 1fr 1fr;gap:16px}
.grid-2x2{display:grid;grid-template-columns:1fr 1fr;gap:12px}
.grid-2x2 label{display:block;font-size:.9rem;font-weight:600;margin-bottom:6px;color:var(--text-primary)}
.grid-2x2 input,.grid-2x2 select{width:100%;padding:10px 14px;border:1px solid var(--border);border-radius:var(--radius);background:var(--bg-secondary);font-size:.95rem;transition:border-color .2s;box-sizing:border-box}
.grid-2x2 input:focus,.grid-2x2 select:focus{outline:none;border-color:var(--accent);box-shadow:0 0 0 3px rgba(37,99,235,.1)}
.card label{display:block;font-size:.9rem;font-weight:600;margin-bottom:6px;color:var(--text-primary)}
.card>input,.card>select,.card>div>input:not([type="hidden"]),.card>div>select{width:100%;padding:10px 14px;border:1px solid var(--border);border-radius:var(--radius);background:var(--bg-secondary);font-size:.95rem;transition:border-color .2s;box-sizing:border-box}

/* ===== Result Box ===== */
.result-box{background:#eff6ff;border:1px solid #bfdbfe;border-radius:var(--radius);padding:24px;margin-top:24px}
.result-box h3{font-size:1rem;font-weight:700;margin-bottom:16px;color:var(--text-primary)}
.result-row{display:flex;justify-content:space-between;align-items:center;padding:8px 0;border-bottom:1px solid #dbeafe}
.result-row:last-child{border-bottom:none}
.result-label{font-size:.9rem;color:var(--text-secondary)}
.result-value{font-size:1.1rem;font-weight:700;color:var(--accent)}
.result-detail{font-size:.8rem;color:var(--text-muted);margin-top:2px}
.result-highlight{font-size:1.6rem;font-weight:700;color:var(--accent);text-align:center;padding:16px 0}

/* ===== Comparison / Data Table ===== */
.comparison-table{width:100%;border-collapse:collapse;margin:20px 0;font-size:.88rem}
.comparison-table th{background:#f1f5f9;font-weight:600;text-align:left;padding:10px 12px;border-bottom:2px solid var(--border);white-space:nowrap}
.comparison-table td{padding:9px 12px;border-bottom:1px solid var(--border)}
.comparison-table tr:hover td{background:#f8fafc}
.table-wrapper{overflow-x:auto;margin:20px 0;border:1px solid var(--border);border-radius:var(--radius)}
.table-wrapper .comparison-table{margin:0}

/* ===== Article Body / How-to & Formula Sections ===== */
.article-body{padding:32px 0}
.article-body h2{font-size:1.3rem;font-weight:700;margin:32px 0 12px;color:var(--text-primary)}
.article-body h3{font-size:1.1rem;font-weight:600;margin:24px 0 8px}
.article-body p{margin-bottom:14px;color:var(--text-secondary);line-height:1.7}
.article-body ul,.article-body ol{margin:0 0 14px 20px;color:var(--text-secondary)}
.article-body li{margin-bottom:6px;list-style:disc}
.article-body ol li{list-style:decimal}

/* ===== Info Box ===== */
.info-box{background:#eff6ff;border-left:4px solid var(--accent);border-radius:0 var(--radius) var(--radius) 0;padding:16px 20px;margin:20px 0;font-size:.9rem;color:var(--text-secondary)}
.info-box strong{color:var(--text-primary)}

/* ===== Ad Placeholder ===== */
.ad-spot{background:#f1f5f9;border:1px dashed #cbd5e1;border-radius:8px;padding:20px;text-align:center;color:#94a3b8;margin:24px 0;min-height:90px;display:flex;align-items:center;justify-content:center;font-size:.85rem}

/* ===== Footer ===== */
.site-footer{background:var(--bg-secondary);border-top:1px solid var(--border);padding:32px 0;margin-top:auto;font-size:.85rem;color:var(--text-muted)}
.footer-inner{display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:12px}
.footer-links{display:flex;gap:20px}
.footer-links a{color:var(--text-muted)}
.footer-links a:hover{color:var(--accent)}

/* ===== Swap Button ===== */
.swap-btn{display:flex;align-items:center;justify-content:center;width:44px;height:44px;border-radius:50%;border:1px solid var(--border);background:var(--bg-secondary);cursor:pointer;font-size:1.2rem;transition:background .2s;margin:0 auto}
.swap-btn:hover{background:#eff6ff;border-color:var(--accent)}

/* ===== Calc Section Divider ===== */
.calc-section{background:var(--bg-card);border:1px solid var(--border);border-radius:var(--radius);padding:24px;margin-bottom:20px;box-shadow:var(--shadow)}
.calc-section h3{font-size:1rem;font-weight:700;margin-bottom:14px;color:var(--text-primary)}

/* ===== Responsive ===== */
@media(max-width:768px){
  .menu-toggle{display:block}
  .nav-links{display:none;position:absolute;top:var(--header-h);left:0;right:0;flex-direction:column;background:var(--bg-secondary);border-bottom:1px solid var(--border);padding:12px 20px;box-shadow:var(--shadow-md);gap:2px}
  .nav-links.open{display:flex}
  .nav-links a{padding:10px 12px;border-radius:var(--radius)}
  .hero h1{font-size:1.5rem}
  .hero{padding:36px 0 32px}
  .form-row,.form-row-3,.grid-2x2{grid-template-columns:1fr}
  .tool-container{padding:20px}
  .result-row{flex-direction:column;align-items:flex-start;gap:2px}
  .footer-inner{flex-direction:column;text-align:center}
  .card-grid{grid-template-columns:1fr}
}
@media(max-width:480px){
  .container{padding:0 14px}
  .hero h1{font-size:1.3rem}
}

/* ===== FAQ Section ===== */
.faq-section{margin:20px 0}
.faq-section details{border:1px solid var(--border);border-radius:var(--radius);margin-bottom:10px;overflow:hidden}
.faq-section summary{padding:14px 18px;cursor:pointer;font-size:.95rem;background:var(--bg-secondary);transition:background .2s;list-style:none}
.faq-section summary::-webkit-details-marker{display:none}
.faq-section summary::before{content:'+';display:inline-block;width:20px;font-weight:700;color:var(--accent);font-size:1.1rem}
.faq-section details[open] summary::before{content:'\2212'}
.faq-section details[open] summary{background:#eff6ff;border-bottom:1px solid var(--border)}
.faq-section details p,.faq-section details ul{padding:14px 18px 14px 38px;margin:0;color:var(--text-secondary);font-size:.9rem;line-height:1.7}
.faq-section details ul{padding-top:0}
.faq-section details li{margin-bottom:4px;list-style:disc}

/* ===== Last Updated ===== */
.last-updated{font-size:.82rem;color:var(--text-muted);margin-bottom:8px;display:flex;align-items:center;gap:6px}
.last-updated::before{content:'🕓';font-size:.85rem}

/* ===== Inline Content Link ===== */
.article-body a.content-link{color:var(--accent);font-weight:500;text-decoration:underline;text-underline-offset:2px}
.article-body a.content-link:hover{color:var(--accent-hover)}

/* ===== Info Graphic (CSS-only) ===== */
.info-graphic{background:var(--bg-secondary);border:1px solid var(--border);border-radius:var(--radius);padding:24px;margin:20px 0}
.info-graphic h4{font-size:.95rem;font-weight:700;margin-bottom:16px;text-align:center;color:var(--text-primary)}
.bar-chart{display:flex;flex-direction:column;gap:10px}
.bar-row{display:flex;align-items:center;gap:12px}
.bar-label{min-width:120px;font-size:.82rem;color:var(--text-secondary);text-align:right}
.bar-fill{height:24px;border-radius:4px;background:var(--accent);position:relative;min-width:8px;transition:width .6s ease}
.bar-fill span{position:absolute;right:8px;top:50%;transform:translateY(-50%);font-size:.75rem;font-weight:600;color:#fff;white-space:nowrap}
.bar-fill.green{background:#22c55e}
.bar-fill.yellow{background:#eab308}
.bar-fill.red{background:#ef4444}
.bar-fill.blue{background:#3b82f6}
.bar-fill.purple{background:#8b5cf6}
@media(max-width:480px){.bar-label{min-width:80px;font-size:.76rem}}

/* ===== Related Calculators Section ===== */
.related-section{padding:32px 0}
.related-section .section-heading{margin-top:0}

/* ===== ZH Page Classes (Chinese calculator pages) ===== */
.calc-card{background:var(--bg-card);border:1px solid var(--border);border-radius:var(--radius);padding:32px;margin:24px 0;box-shadow:var(--shadow)}
.input-group{margin-bottom:18px}
.input-group label{display:block;font-size:.9rem;font-weight:600;margin-bottom:6px;color:var(--text-primary)}
.input-group input,.input-group select{width:100%;padding:10px 14px;border:1px solid var(--border);border-radius:var(--radius);background:var(--bg-secondary);font-size:.95rem;transition:border-color .2s}
.input-group input:focus,.input-group select:focus{outline:none;border-color:var(--accent);box-shadow:0 0 0 3px rgba(37,99,235,.1)}
.page-subtitle{font-size:1.05rem;color:var(--text-secondary);margin-bottom:12px}
.result-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(180px,1fr));gap:16px;margin-top:16px}
.result-item{background:var(--bg-secondary);border:1px solid #bfdbfe;border-radius:var(--radius);padding:16px;text-align:center}
.result-item .result-label{display:block;font-size:.85rem;color:var(--text-secondary);margin-bottom:6px}
.result-item .result-value{display:block;font-size:1.25rem;font-weight:700;color:var(--accent)}
.info-table{width:100%;border-collapse:collapse;margin:20px 0;font-size:.88rem}
.info-table th{background:#f1f5f9;font-weight:600;text-align:left;padding:10px 12px;border-bottom:2px solid var(--border)}
.info-table td{padding:9px 12px;border-bottom:1px solid var(--border)}
.info-table tr:hover td{background:#f8fafc}
.faq-item{border:1px solid var(--border);border-radius:var(--radius);margin-bottom:10px;overflow:hidden}
.faq-q{width:100%;text-align:left;padding:14px 18px;background:var(--bg-secondary);border:none;cursor:pointer;font-size:.95rem;font-weight:500;color:var(--text-primary);transition:background .2s;display:flex;justify-content:space-between;align-items:center}
.faq-q::after{content:'+';font-weight:700;color:var(--accent);font-size:1.1rem;flex-shrink:0}
.faq-q.open{background:#eff6ff;border-bottom:1px solid var(--border)}
.faq-q.open::after{content:'\2212'}
.faq-a{display:none;padding:14px 18px;color:var(--text-secondary);font-size:.9rem;line-height:1.7}
.faq-a.open{display:block}
.faq-a p{margin-bottom:10px}
.faq-a p:last-child{margin-bottom:0}
.btn-primary{background:var(--accent);color:#fff;border-color:var(--accent);display:inline-flex;align-items:center;justify-content:center;padding:10px 22px;border-radius:var(--radius);font-weight:600;font-size:.95rem;border:1px solid var(--accent);cursor:pointer;transition:background .2s,border-color .2s}
.btn-primary:hover{background:var(--accent-hover);border-color:var(--accent-hover)}
@media(max-width:768px){
  .calc-card{padding:20px}
  .result-grid{grid-template-columns:1fr 1fr}
}
@media(max-width:480px){
  .result-grid{grid-template-columns:1fr}
}

/* ===== UI/UX Improvements ===== */

/* Accessibility: focus-visible states */
a:focus-visible,.btn:focus-visible,summary:focus-visible,.nav-links a:focus-visible{outline:2px solid var(--accent);outline-offset:2px;border-radius:var(--radius)}
input:focus-visible,select:focus-visible{outline:2px solid var(--accent);outline-offset:0}

/* Article h2 accent underline */
.article-body h2{position:relative;padding-bottom:8px}
.article-body h2::after{content:'';position:absolute;left:0;bottom:0;width:40px;height:3px;background:var(--accent);border-radius:2px}

/* Smooth card entrance animation */
@keyframes fadeInUp{from{opacity:0;transform:translateY(12px)}to{opacity:1;transform:translateY(0)}}
.card-grid .card{animation:fadeInUp .4s ease-out both}
.card-grid .card:nth-child(2){animation-delay:.08s}
.card-grid .card:nth-child(3){animation-delay:.16s}
.card-grid .card:nth-child(4){animation-delay:.24s}

/* Better CTA button hover */
.article-body a[style*="background:var(--accent)"]:hover{filter:brightness(1.1);transform:translateY(-1px)}

/* Smoother nav transition on mobile */
.nav-links{transition:opacity .2s ease}

/* Back-to-top scroll indicator */
.site-footer{scroll-margin-top:var(--header-h)}

/* Prefers reduced motion */
@media(prefers-reduced-motion:reduce){
  *{animation-duration:0s!important;transition-duration:0s!important}
  html{scroll-behavior:auto}
}

/* ===== Print Styles ===== */
@media print{
  *{color:#000!important;background:#fff!important;box-shadow:none!important;text-shadow:none!important}
  body{font-size:12pt;line-height:1.5}
  .site-header,.site-footer,.menu-toggle,.dark-mode-btn,.ad-spot,.breadcrumb,
  #darkModeToggle,.nav-links,.card-grid,.bar-chart,canvas{display:none!important}
  .container{max-width:100%;padding:0}
  .calc-card{border:1px solid #ccc;padding:16px;page-break-inside:avoid}
  .result-box{border:1px solid #999;padding:12px;page-break-inside:avoid}
  h1{font-size:18pt;margin-bottom:8pt}
  h2{font-size:14pt;margin-top:16pt;margin-bottom:6pt;page-break-after:avoid}
  h3{font-size:12pt;page-break-after:avoid}
  table{border-collapse:collapse;width:100%}
  th,td{border:1px solid #ccc;padding:6px 8px;font-size:10pt}
  a{text-decoration:underline}
  a[href^="http"]::after{content:" (" attr(href) ")";font-size:9pt;color:#666!important}
  .info-table{page-break-inside:avoid}
  .faq-a{display:block!important}
  .article-body{max-width:100%}
  @page{margin:2cm}
}