:root{
  --bg:#ffffff;
  --bg-alt:#f7f8fa;
  --text:#1a1d23;
  --text-soft:#5b6270;
  --text-faint:#8a8f99;
  --border:#e4e6eb;
  --accent:#2563eb;
  --accent-dark:#1d4ed8;
  --radius:10px;
  --radius-sm:6px;
  --shadow:0 2px 10px rgba(20,20,30,0.06);
  --shadow-lg:0 12px 40px rgba(20,20,30,0.16);
  --maxw:1180px;

  --c-alkali-metal:#ffd6cc;
  --c-alkaline-earth:#ffe6b3;
  --c-transition-metal:#ffe9a3;
  --c-post-transition-metal:#cdeccb;
  --c-metalloid:#bfe8e0;
  --c-nonmetal:#bfe0f7;
  --c-noble-gas:#d6c8f5;
  --c-lanthanide:#ffd1e6;
  --c-actinide:#ffc2d9;
  --c-unknown:#e6e6e6;

  --t-alkali-metal:#7a2c12;
  --t-alkaline-earth:#7a5200;
  --t-transition-metal:#7a5c00;
  --t-post-transition-metal:#1f5c1f;
  --t-metalloid:#0d5c50;
  --t-nonmetal:#0d4a7a;
  --t-noble-gas:#3f2a7a;
  --t-lanthanide:#7a1f4a;
  --t-actinide:#7a1130;
  --t-unknown:#444;
}

*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Inter",Helvetica,Arial,sans-serif;
  background:var(--bg);
  color:var(--text);
  line-height:1.6;
  -webkit-font-smoothing:antialiased;
}
img{max-width:100%;display:block}
a{color:var(--accent);text-decoration:none}
a:hover{text-decoration:underline}
.container{max-width:var(--maxw);margin:0 auto;padding:0 20px}
.visually-hidden{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0,0,0,0)}

/* Header */
header.site-header{
  border-bottom:1px solid var(--border);
  position:sticky;top:0;background:rgba(255,255,255,0.96);
  backdrop-filter:blur(6px);
  z-index:50;
}
.header-inner{display:flex;align-items:center;justify-content:space-between;padding:14px 20px;max-width:var(--maxw);margin:0 auto}
.logo{font-size:18px;font-weight:700;color:var(--text);display:flex;align-items:center;gap:8px}
.logo span{color:var(--accent)}
nav.main-nav{display:flex;gap:24px;align-items:center}
nav.main-nav a{color:var(--text-soft);font-weight:500;font-size:14.5px}
nav.main-nav a:hover{color:var(--accent);text-decoration:none}
.nav-toggle{display:none;background:none;border:none;font-size:24px;cursor:pointer;color:var(--text)}

@media (max-width:760px){
  nav.main-nav{
    position:absolute;top:100%;left:0;right:0;
    background:var(--bg);border-bottom:1px solid var(--border);
    flex-direction:column;align-items:flex-start;padding:14px 20px;gap:14px;
    display:none;
  }
  nav.main-nav.open{display:flex}
  .nav-toggle{display:block}
}

/* Hero */
.hero{padding:42px 20px 24px;text-align:center;max-width:760px;margin:0 auto}
.hero h1{font-size:clamp(24px,4vw,34px);margin:0 0 10px;font-weight:700;letter-spacing:-0.01em}
.hero p{color:var(--text-soft);font-size:16px;margin:0 0 20px}
.hero-actions{display:flex;gap:10px;justify-content:center;flex-wrap:wrap}

.btn{
  display:inline-flex;align-items:center;gap:6px;
  padding:10px 18px;border-radius:8px;font-weight:600;font-size:14.5px;
  border:1px solid var(--border);cursor:pointer;background:var(--bg);color:var(--text);
  transition:transform .12s ease, box-shadow .12s ease;
}
.btn:hover{box-shadow:var(--shadow);text-decoration:none}
.btn:active{transform:scale(0.97)}
.btn-primary{background:var(--accent);color:#fff;border-color:var(--accent)}
.btn-primary:hover{background:var(--accent-dark)}
.btn-ghost{background:transparent}
.btn svg{width:16px;height:16px}

/* Controls bar above table */
.controls{
  display:flex;flex-wrap:wrap;gap:10px;align-items:center;justify-content:center;
  margin:0 0 22px;padding:0 20px;
}
.controls select, .controls input[type="text"]{
  padding:8px 12px;border:1px solid var(--border);border-radius:8px;font-size:14px;
  background:var(--bg);color:var(--text);
}
.legend{display:flex;flex-wrap:wrap;gap:8px;justify-content:center;margin:0 0 28px;padding:0 20px}
.legend-item{display:flex;align-items:center;gap:6px;font-size:12px;color:var(--text-soft)}
.legend-swatch{width:12px;height:12px;border-radius:3px}

/* Periodic Table Grid */
.table-wrap{overflow-x:auto;padding:0 12px 30px}
.ptable{
  display:grid;
  grid-template-columns:repeat(18,minmax(40px,1fr));
  gap:3px;
  max-width:1400px;
  margin:0 auto;
  min-width:760px;
}
.cell{
  aspect-ratio:1/1;
  border-radius:6px;
  display:flex;flex-direction:column;align-items:center;justify-content:center;
  cursor:pointer;
  border:1px solid rgba(0,0,0,0.06);
  position:relative;
  transition:transform .1s ease, box-shadow .1s ease;
  padding:2px;
  overflow:hidden;
}
.cell:hover{transform:translateY(-2px) scale(1.06);box-shadow:0 4px 14px rgba(0,0,0,0.18);z-index:5}
.cell:focus-visible{outline:2px solid var(--accent);outline-offset:2px}
.cell .num{font-size:9px;align-self:flex-start;margin-left:3px;opacity:0.75}
.cell .sym{font-size:clamp(13px,2vw,18px);font-weight:700;line-height:1}
.cell .name{font-size:7px;opacity:0.8;display:none}
@media (min-width:700px){.cell .name{display:block}}
.cell.placeholder{visibility:hidden}
.cell.dim{opacity:0.18;transform:none}
.cell.lanth-actin-link{font-size:9px}

/* category coloring */
.cell.alkali-metal{background:var(--c-alkali-metal);color:var(--t-alkali-metal)}
.cell.alkaline-earth{background:var(--c-alkaline-earth);color:var(--t-alkaline-earth)}
.cell.transition-metal{background:var(--c-transition-metal);color:var(--t-transition-metal)}
.cell.post-transition-metal{background:var(--c-post-transition-metal);color:var(--t-post-transition-metal)}
.cell.metalloid{background:var(--c-metalloid);color:var(--t-metalloid)}
.cell.nonmetal{background:var(--c-nonmetal);color:var(--t-nonmetal)}
.cell.noble-gas{background:var(--c-noble-gas);color:var(--t-noble-gas)}
.cell.lanthanide{background:var(--c-lanthanide);color:var(--t-lanthanide)}
.cell.actinide{background:var(--c-actinide);color:var(--t-actinide)}
.cell.unknown{background:var(--c-unknown);color:var(--t-unknown)}

/* Modal */
.modal-overlay{
  position:fixed;inset:0;background:rgba(15,17,22,0.55);
  display:none;align-items:center;justify-content:center;z-index:200;padding:16px;
}
.modal-overlay.open{display:flex}
.modal{
  background:var(--bg);border-radius:14px;max-width:480px;width:100%;
  max-height:86vh;overflow-y:auto;box-shadow:var(--shadow-lg);
  padding:24px;position:relative;
}
.modal-close{
  position:absolute;top:14px;right:14px;background:var(--bg-alt);border:none;
  width:32px;height:32px;border-radius:50%;font-size:18px;cursor:pointer;color:var(--text-soft);
}
.modal-close:hover{background:var(--border)}
.modal-head{display:flex;align-items:center;gap:16px;margin-bottom:16px}
.modal-symbol{
  width:64px;height:64px;border-radius:10px;display:flex;align-items:center;justify-content:center;
  font-size:28px;font-weight:700;flex-shrink:0;
}
.modal-head h2{margin:0;font-size:21px}
.modal-head .modal-meta{color:var(--text-soft);font-size:13px;margin-top:2px}
.modal-props{display:grid;grid-template-columns:1fr 1fr;gap:10px;margin:16px 0}
.prop{background:var(--bg-alt);border-radius:8px;padding:8px 10px}
.prop .k{font-size:11px;color:var(--text-faint);margin-bottom:2px}
.prop .v{font-size:14px;font-weight:600}
.modal-summary{font-size:14px;color:var(--text-soft);margin:14px 0;line-height:1.65}
.modal-actions{display:flex;gap:8px;margin-top:14px;flex-wrap:wrap}

/* Sections */
section{padding:50px 20px}
section.alt{background:var(--bg-alt)}
h2.section-title{font-size:26px;margin:0 0 8px;text-align:center}
p.section-sub{text-align:center;color:var(--text-soft);margin:0 0 32px;max-width:600px;margin-inline:auto}

.feature-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:18px;max-width:var(--maxw);margin:0 auto}
.feature-card{background:var(--bg);border:1px solid var(--border);border-radius:var(--radius);padding:20px}
.feature-card h3{margin:0 0 6px;font-size:16px}
.feature-card p{margin:0;color:var(--text-soft);font-size:14px}
.feature-card .icon{font-size:22px;margin-bottom:10px}

/* FAQ */
.faq{max-width:720px;margin:0 auto}
details{border:1px solid var(--border);border-radius:8px;padding:14px 16px;margin-bottom:10px;background:var(--bg)}
details summary{cursor:pointer;font-weight:600;font-size:15px}
details p{margin:10px 0 0;color:var(--text-soft);font-size:14px}

/* Footer */
footer{border-top:1px solid var(--border);padding:36px 20px;color:var(--text-soft);font-size:13.5px}
.footer-inner{max-width:var(--maxw);margin:0 auto;display:flex;flex-wrap:wrap;gap:24px;justify-content:space-between}
.footer-col h4{font-size:13px;color:var(--text);margin:0 0 10px}
.footer-col a{display:block;color:var(--text-soft);margin-bottom:6px;font-size:13.5px}
.footer-col a:hover{color:var(--accent)}
.footer-bottom{text-align:center;margin-top:24px;padding-top:18px;border-top:1px solid var(--border);font-size:12.5px;color:var(--text-faint)}

/* Blog list */
.blog-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(260px,1fr));gap:20px;max-width:var(--maxw);margin:0 auto}
.blog-card{border:1px solid var(--border);border-radius:var(--radius);padding:18px;background:var(--bg)}
.blog-card .tag{font-size:11px;color:var(--accent);font-weight:700;text-transform:uppercase;letter-spacing:.04em}
.blog-card h3{margin:8px 0 6px;font-size:17px}
.blog-card p{color:var(--text-soft);font-size:14px;margin:0 0 10px}
.blog-card .date{font-size:12px;color:var(--text-faint)}

/* Blog post article */
article.post{max-width:680px;margin:0 auto;padding:40px 20px}
article.post h1{font-size:30px;margin:0 0 8px}
article.post .post-meta{color:var(--text-faint);font-size:13px;margin-bottom:24px}
article.post h2{font-size:21px;margin:32px 0 10px}
article.post p{font-size:15.5px;color:#333;margin:0 0 16px}
article.post ul{font-size:15.5px;color:#333}

/* Quiz page */
.quiz-card{max-width:560px;margin:0 auto;background:var(--bg);border:1px solid var(--border);border-radius:var(--radius);padding:28px;box-shadow:var(--shadow)}
.quiz-progress{font-size:13px;color:var(--text-faint);margin-bottom:6px}
.quiz-q{font-size:19px;font-weight:600;margin:0 0 18px}
.quiz-options{display:grid;gap:10px}
.quiz-opt{padding:12px 14px;border:1px solid var(--border);border-radius:8px;cursor:pointer;font-size:15px;text-align:left;background:var(--bg);transition:background .12s}
.quiz-opt:hover{background:var(--bg-alt)}
.quiz-opt.correct{background:#d8f3dc;border-color:#52b788}
.quiz-opt.wrong{background:#ffd6d6;border-color:#e07a7a}
.quiz-result{text-align:center}
.quiz-result .score{font-size:42px;font-weight:700;color:var(--accent);margin:10px 0}

@media (max-width:600px){
  .modal-props{grid-template-columns:1fr 1fr}
  .hero h1{font-size:24px}
}