@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@400;500;600;700;800&display=swap');
@import url('https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400;500;700&display=swap');

/* =====================================================================
   CalcStack — dark design system (Poppins · violet)
   Visual restyle only. No calculator markup IDs or JS hooks changed.
   ===================================================================== */
:root{
  /* surfaces */
  --bg:#0a0d15;            /* page base */
  --bg-grid:#10141f;       /* hero panel */
  --card:#11151f;          /* default surface */
  --card-2:#161b27;        /* elevated surface */
  --field:#0c1019;         /* inputs */
  --line:#222838;          /* hairline border */
  --line-soft:#1a1f2d;

  /* ink */
  --ink:#eef1f8;           /* primary text */
  --ink-soft:#b9c0d4;      /* secondary text */
  --muted:#737b92;         /* tertiary / labels */

  /* brand */
  --accent:#8b7bff;        /* violet, tuned for dark */
  --accent-bright:#a99bff;
  --accent-weak:rgba(139,123,255,.12);
  --accent-line:rgba(139,123,255,.34);
  --accent-glow:rgba(139,123,255,.22);
  --good:#3ddc97;
  --amber:#f4b14d;

  --radius:14px;
  --radius-sm:10px;
  --mono:'JetBrains Mono',ui-monospace,'SF Mono','Cascadia Code',Menlo,Consolas,monospace;
  --sans:'Poppins',-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;
  --shadow:0 1px 0 rgba(255,255,255,.02) inset,0 12px 28px -18px rgba(0,0,0,.8);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;font-family:var(--sans);color:var(--ink);background:var(--bg);
  line-height:1.65;-webkit-font-smoothing:antialiased;text-rendering:optimizeLegibility;
  background-image:
    radial-gradient(900px 460px at 78% -8%,rgba(139,123,255,.10),transparent 60%),
    radial-gradient(700px 380px at 0% 0%,rgba(139,123,255,.05),transparent 55%);
  background-attachment:fixed;
}
a{color:var(--accent-bright);text-decoration:none}
a:hover{color:var(--accent);text-decoration:none}
::selection{background:var(--accent-weak);color:#fff}
code{font-family:var(--mono);font-size:.9em;background:var(--card-2);border:1px solid var(--line-soft);
  padding:.08em .4em;border-radius:6px;color:var(--accent-bright)}
.wrap{max-width:940px;margin:0 auto;padding:0 22px}

/* ---------- header ---------- */
.site-head{
  border-bottom:1px solid var(--line);position:sticky;top:0;z-index:30;
  background:rgba(10,13,21,.72);backdrop-filter:saturate(150%) blur(12px);
  -webkit-backdrop-filter:saturate(150%) blur(12px);
}
.site-head .wrap{display:flex;align-items:center;justify-content:space-between;height:64px}
.brand{font-weight:800;font-size:18px;letter-spacing:-.02em;color:var(--ink);
  display:flex;align-items:center;gap:11px}
.brand .mk{
  font-family:var(--mono);font-weight:700;font-size:13px;color:var(--accent-bright);
  width:30px;height:30px;display:inline-flex;align-items:center;justify-content:center;
  background:linear-gradient(180deg,rgba(139,123,255,.20),rgba(139,123,255,.06));
  border:1px solid var(--accent-line);border-radius:9px;
  box-shadow:0 0 0 1px rgba(0,0,0,.4) inset,0 6px 18px -10px var(--accent-glow);
}
.nav{display:flex;align-items:center;gap:4px}
.nav a{color:var(--ink-soft);font-size:13.5px;font-weight:600;padding:7px 12px;border-radius:8px;
  transition:color .14s,background .14s}
.nav a:hover{color:var(--ink);background:var(--card-2)}

/* ---------- breadcrumb ---------- */
.crumb{font-family:var(--mono);font-size:12.5px;color:var(--muted);padding:24px 0 2px;letter-spacing:.01em}
.crumb a{color:var(--muted)}
.crumb a:hover{color:var(--accent-bright)}
.crumb span{color:var(--ink-soft)}

/* ---------- headings ---------- */
h1{font-size:clamp(28px,4.4vw,42px);line-height:1.1;letter-spacing:-.03em;margin:.25em 0 .35em;font-weight:800}
h2{font-size:21px;letter-spacing:-.015em;margin:1.9em 0 .55em;font-weight:700}
h3{font-size:16px;margin:1.4em 0 .3em;font-weight:700}
.lede{font-size:18px;color:var(--ink-soft);margin:0 0 8px;max-width:62ch}
.lede code{font-size:.85em}

/* ---------- tool card ---------- */
.tool{
  background:linear-gradient(180deg,var(--card-2),var(--card));
  border:1px solid var(--line);border-radius:var(--radius);
  padding:24px;margin:26px 0 10px;box-shadow:var(--shadow);position:relative;
}
.tool::before{content:"";position:absolute;inset:0 0 auto 0;height:1px;border-radius:var(--radius) var(--radius) 0 0;
  background:linear-gradient(90deg,transparent,var(--accent-line),transparent)}
.row{display:flex;flex-wrap:wrap;gap:16px}
.field{flex:1;min-width:150px;display:flex;flex-direction:column;gap:7px}
label{font-size:12px;font-weight:600;color:var(--muted);text-transform:uppercase;letter-spacing:.06em}
input,select{
  font-family:var(--mono);font-size:16px;padding:12px 13px;border:1px solid var(--line);
  border-radius:var(--radius-sm);background:var(--field);color:var(--ink);width:100%;
  transition:border-color .14s,box-shadow .14s;
}
input::placeholder{color:#525a72}
input:hover,select:hover{border-color:#2e364a}
input:focus,select:focus{outline:none;border-color:var(--accent);box-shadow:0 0 0 3px var(--accent-weak)}
select{appearance:none;-webkit-appearance:none;cursor:pointer;
  background-image:linear-gradient(45deg,transparent 50%,var(--muted) 50%),linear-gradient(135deg,var(--muted) 50%,transparent 50%);
  background-position:calc(100% - 17px) 19px,calc(100% - 12px) 19px;background-size:5px 5px,5px 5px;background-repeat:no-repeat;padding-right:34px}
input[type=date]{cursor:pointer}
input[type=date]::-webkit-calendar-picker-indicator{filter:invert(.7);cursor:pointer}

.btn{
  font-family:var(--sans);font-weight:700;font-size:14.5px;cursor:pointer;border:1px solid transparent;
  background:linear-gradient(180deg,var(--accent-bright),var(--accent));color:#08111f;
  padding:12px 22px;border-radius:var(--radius-sm);margin-top:14px;margin-right:10px;
  box-shadow:0 8px 20px -10px var(--accent-glow);transition:transform .1s,box-shadow .14s,filter .14s;
}
.btn:hover{filter:brightness(1.06);box-shadow:0 10px 26px -10px var(--accent-glow)}
.btn:active{transform:translateY(1px)}
.btn.ghost{background:transparent;color:var(--accent-bright);border-color:var(--line);box-shadow:none}
.btn.ghost:hover{border-color:var(--accent-line);background:var(--accent-weak);filter:none}

/* ---------- result ---------- */
.result{
  margin-top:20px;background:var(--field);border:1px solid var(--line);border-radius:12px;
  padding:18px 20px;font-size:15px;display:none;position:relative;overflow:hidden;
}
.result::before{content:"";position:absolute;left:0;top:0;bottom:0;width:3px;
  background:linear-gradient(180deg,var(--accent-bright),var(--accent))}
.result.show{display:block;animation:pop .28s cubic-bezier(.2,.7,.3,1)}
@keyframes pop{from{transform:translateY(6px);opacity:0}to{transform:none;opacity:1}}
.result .big{font-family:var(--mono);font-size:27px;font-weight:700;color:var(--ink);line-height:1.25;letter-spacing:-.01em}
.result .sub{color:var(--ink-soft);font-size:14px;margin-top:6px}
.steps{font-family:var(--mono);font-size:12.5px;line-height:1.7;white-space:pre;overflow:auto;
  background:#080b12;border:1px solid var(--line-soft);border-radius:var(--radius-sm);
  padding:14px;margin-top:14px;color:var(--ink-soft)}
.steps::-webkit-scrollbar{height:8px}
.steps::-webkit-scrollbar-thumb{background:#2a3147;border-radius:8px}
.err{color:#ff7a85;font-size:13.5px;margin-top:10px;min-height:18px;font-weight:500}

/* ---------- prose ---------- */
.prose{margin-top:14px}
.prose p{margin:.65em 0;color:var(--ink-soft)}
.prose strong{color:var(--ink);font-weight:700}
.prose em{color:var(--accent-bright);font-style:normal;font-weight:600}
.prose .formula{font-family:var(--mono);background:var(--card-2);border:1px solid var(--line);
  border-radius:var(--radius-sm);padding:13px 16px;display:inline-block;margin:8px 0;color:var(--accent-bright);font-size:14px}
details{border:1px solid var(--line);border-radius:var(--radius-sm);padding:0 16px;margin:9px 0;
  background:var(--card);transition:border-color .14s}
details[open]{border-color:#2a3247}
details summary{font-weight:600;cursor:pointer;padding:14px 0;list-style:none;color:var(--ink);
  display:flex;align-items:center;gap:10px}
details summary::-webkit-details-marker{display:none}
details summary::before{content:'+';color:var(--accent-bright);font-family:var(--mono);font-weight:700;
  width:18px;height:18px;display:inline-flex;align-items:center;justify-content:center;
  border:1px solid var(--accent-line);border-radius:5px;font-size:13px;flex:0 0 18px}
details[open] summary::before{content:'–'}
details p{margin:0 0 15px;color:var(--ink-soft)}

/* ---------- homepage hero ---------- */
.hero{
  position:relative;margin:30px 0 6px;padding:56px 36px;border-radius:20px;overflow:hidden;
  background:
    radial-gradient(700px 320px at 85% -30%,rgba(139,123,255,.20),transparent 62%),
    linear-gradient(180deg,#10141f,#0c0f18);
  border:1px solid var(--line);
}
.hero::before{content:"";position:absolute;inset:0;opacity:.5;pointer-events:none;
  background-image:linear-gradient(var(--line-soft) 1px,transparent 1px),linear-gradient(90deg,var(--line-soft) 1px,transparent 1px);
  background-size:34px 34px;
  -webkit-mask-image:radial-gradient(620px 360px at 70% 0%,#000,transparent 75%);
  mask-image:radial-gradient(620px 360px at 70% 0%,#000,transparent 75%);
}
.hero>*{position:relative}
.kicker{display:inline-flex;align-items:center;gap:8px;font-family:var(--mono);font-size:12px;
  font-weight:500;letter-spacing:.03em;color:var(--accent-bright);background:var(--accent-weak);
  border:1px solid var(--accent-line);padding:6px 13px;border-radius:30px;margin-bottom:20px;
  white-space:nowrap;max-width:100%}
.kicker .dot{flex:0 0 6px}
.kicker .dot{width:6px;height:6px;border-radius:50%;background:var(--good);box-shadow:0 0 8px var(--good)}
.hero h1{margin:0 0 14px;max-width:18ch}
.hero .lede{font-size:19px;max-width:56ch}
.stats{display:flex;flex-wrap:wrap;gap:28px;margin-top:26px}
.stats .stat{display:flex;flex-direction:column;gap:2px}
.stats .stat b{font-family:var(--mono);font-size:20px;color:var(--ink);font-weight:700}
.stats .stat span{font-size:12.5px;color:var(--muted)}

/* ---------- section label ---------- */
.sec-head{display:flex;align-items:baseline;gap:12px;margin:2em 0 .2em}
.sec-head h2{margin:0}
.sec-head .count{font-family:var(--mono);font-size:12px;color:var(--muted);white-space:nowrap;
  border:1px solid var(--line);border-radius:20px;padding:2px 10px}

/* ---------- category grid ---------- */
.grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(250px,1fr));gap:16px;margin:18px 0 10px}
.cat{display:flex;flex-direction:column;background:linear-gradient(180deg,var(--card-2),var(--card));
  border:1px solid var(--line);border-radius:var(--radius);padding:20px;
  transition:transform .14s,border-color .14s,box-shadow .14s;position:relative}
.cat:hover{transform:translateY(-3px);border-color:var(--accent-line);
  box-shadow:0 18px 36px -22px var(--accent-glow);text-decoration:none}
.cat .ico{width:42px;height:42px;border-radius:11px;display:flex;align-items:center;justify-content:center;
  background:linear-gradient(180deg,rgba(139,123,255,.16),rgba(139,123,255,.04));
  border:1px solid var(--accent-line);margin-bottom:14px}
.cat .ico svg{width:21px;height:21px;stroke:var(--accent-bright);stroke-width:1.7;fill:none;
  stroke-linecap:round;stroke-linejoin:round}
.cat .tag{font-family:var(--mono);font-size:11.5px;color:var(--muted);font-weight:500;letter-spacing:.02em}
.cat h3{margin:7px 0 5px;color:var(--ink);font-size:16.5px}
.cat p{margin:0;color:var(--muted);font-size:13.5px;line-height:1.55}
.cat .go{margin-top:auto;padding-top:14px;font-family:var(--mono);font-size:12px;color:var(--accent-bright);
  display:inline-flex;align-items:center;gap:6px;opacity:0;transform:translateX(-4px);transition:opacity .14s,transform .14s}
.cat:hover .go{opacity:1;transform:none}

/* ---------- related ---------- */
.related{display:flex;flex-wrap:wrap;gap:10px;margin:10px 0 30px}
.related a{background:var(--card-2);color:var(--ink-soft);font-size:13px;font-weight:600;
  padding:9px 14px;border-radius:24px;border:1px solid var(--line);transition:all .14s}
.related a:hover{text-decoration:none;color:var(--accent-bright);border-color:var(--accent-line);background:var(--accent-weak)}

/* ---------- footer ---------- */
.site-foot{border-top:1px solid var(--line);margin-top:54px;background:var(--bg-grid)}
.foot-grid{display:grid;grid-template-columns:1.7fr 1fr 1fr 1.4fr;gap:30px;padding:42px 22px 30px;align-items:start}
.foot-brand .brand{margin-bottom:13px}
.foot-brand p{color:var(--muted);font-size:13.5px;margin:0;max-width:36ch;line-height:1.6}
.foot-col h4{font-size:11.5px;text-transform:uppercase;letter-spacing:.08em;color:var(--ink-soft);margin:3px 0 14px;font-weight:700}
.foot-col a{display:block;color:var(--muted);font-size:13.5px;padding:5px 0;transition:color .14s}
.foot-col a:hover{color:var(--accent-bright)}
.foot-col p{color:var(--muted);font-size:13px;margin:0 0 12px;line-height:1.55;max-width:30ch}
.foot-col .report{display:inline-flex;align-items:center;gap:7px;white-space:nowrap;font-family:var(--mono);font-size:12.5px;color:var(--accent-bright);
  border:1px solid var(--accent-line);border-radius:9px;padding:9px 13px;background:var(--accent-weak);transition:filter .14s}
.foot-col .report:hover{filter:brightness(1.12)}
.foot-base{display:flex;justify-content:space-between;flex-wrap:wrap;gap:8px;
  padding:18px 22px;border-top:1px solid var(--line-soft);color:var(--muted);font-size:12.5px}
@media(max-width:760px){.foot-grid{grid-template-columns:1fr 1fr;gap:26px}}
@media(max-width:430px){.foot-grid{grid-template-columns:1fr;gap:24px}}

/* ---------- section-head links + small hero (category pages) ---------- */
.sec-head h2 a{color:inherit;text-decoration:none;transition:color .14s}
.sec-head h2 a:hover{color:var(--accent-bright)}
a.count{text-decoration:none;transition:color .14s,border-color .14s}
a.count:hover{color:var(--accent-bright);border-color:var(--accent-line)}
.hero-sm{padding:42px 34px;margin-bottom:18px}
.hero-sm h1{margin:0 0 12px}

/* ---------- mobile hamburger menu (CSS-only toggle) ---------- */
.nav-toggle{display:none}
.nav-burger{display:none}

/* ---------- responsive: tablet & mobile (hamburger below 820px) ---------- */
@media(max-width:820px){
  .wrap{padding:0 18px}
  .site-head .wrap{flex-wrap:wrap;height:auto;min-height:60px;padding-top:11px;padding-bottom:11px}
  .brand{flex:1 1 auto}
  /* burger button */
  .nav-burger{display:flex;flex-direction:column;justify-content:center;gap:5px;
    width:44px;height:40px;padding:0 12px;cursor:pointer;border:1px solid var(--line);
    border-radius:10px;background:var(--card-2);transition:border-color .14s,background .14s}
  .nav-burger:hover{border-color:var(--accent-line)}
  .nav-burger span{display:block;height:2px;width:100%;background:var(--ink-soft);border-radius:2px;
    transition:transform .22s ease,opacity .18s ease}
  /* nav collapses into a dropdown panel */
  .nav{display:none;order:3;flex-basis:100%;flex-direction:column;gap:2px;
    margin-top:11px;padding-top:10px;border-top:1px solid var(--line)}
  .nav a{padding:12px 13px;font-size:15px;border-radius:9px;width:100%}
  .nav-toggle:checked ~ .nav{display:flex;animation:navdrop .2s ease}
  /* morph burger → X when open */
  .nav-toggle:checked ~ .nav-burger{background:var(--accent-weak);border-color:var(--accent-line)}
  .nav-toggle:checked ~ .nav-burger span:nth-child(1){transform:translateY(7px) rotate(45deg)}
  .nav-toggle:checked ~ .nav-burger span:nth-child(2){opacity:0}
  .nav-toggle:checked ~ .nav-burger span:nth-child(3){transform:translateY(-7px) rotate(-45deg)}
  .hero{padding:44px 26px}
}
@keyframes navdrop{from{opacity:0;transform:translateY(-6px)}to{opacity:1;transform:none}}

/* ---------- responsive: mobile ---------- */
@media(max-width:560px){
  .hero{padding:36px 20px}
  .kicker{white-space:normal;line-height:1.5}
  .stats{gap:20px}
  .result .big{font-size:22px}
  .btn{margin-right:6px}
}

/* ---------- responsive: narrow phones ---------- */
@media(max-width:430px){
  .hero{padding:32px 18px;border-radius:16px}
  .hero h1{font-size:30px}
}