/* ============================================================
   Cylinder Volume Calculator — Instrument / Blueprint theme
   Mobile-first. Design tokens drive the whole site.
   ============================================================ */

:root{
  /* palette — drafting ink, precise teal, gauge amber */
  --ink:#0b1f33;          /* deep blueprint navy (near-black text/header) */
  --ink-2:#22364b;        /* secondary ink */
  --muted:#5c6f82;        /* muted text */
  --line:#d9e2ec;         /* cool hairline */
  --line-2:#eef2f7;       /* faint hairline */
  --paper:#f5f8fb;        /* cool page background */
  --surface:#ffffff;      /* cards */
  --surface-2:#f0f5fa;    /* insets */
  --brand:#0e7c86;        /* precise teal — primary action */
  --brand-strong:#0a5c64; /* pressed */
  --brand-tint:#e2f2f3;   /* teal wash */
  --accent:#e08a00;       /* gauge amber — the answer readout */
  --accent-tint:#fff3df;
  --good:#137a4b;
  --bad:#b42318;
  --bad-tint:#fdeceb;

  /* type */
  --f-display:"Space Grotesk",-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;
  --f-body:"IBM Plex Sans",-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,sans-serif;
  --f-mono:"IBM Plex Mono",ui-monospace,"SFMono-Regular",Menlo,monospace;

  /* scale */
  --r:12px;               /* radius */
  --r-sm:8px;
  --shadow:0 1px 2px rgba(11,31,51,.06),0 8px 24px rgba(11,31,51,.06);
  --shadow-sm:0 1px 2px rgba(11,31,51,.08);
  --wrap:1140px;
  --gap:clamp(1rem,3vw,1.75rem);
}

*,*::before,*::after{box-sizing:border-box}
html{-webkit-text-size-adjust:100%;scroll-behavior:smooth}
@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}
  *,*::before,*::after{animation-duration:.001ms!important;transition-duration:.001ms!important}}

body{
  margin:0;
  font-family:var(--f-body);
  color:var(--ink);
  background:var(--paper);
  line-height:1.62;
  font-size:clamp(15px,1.6vw,16.5px);
  -webkit-font-smoothing:antialiased;
  text-rendering:optimizeLegibility;
}

/* ---------- layout ---------- */
.wrap{max-width:var(--wrap);margin-inline:auto;padding-inline:clamp(1rem,4vw,2rem)}
.section{padding-block:clamp(2.25rem,6vw,3.75rem)}
.section--tight{padding-block:clamp(1.5rem,4vw,2.25rem)}
main{display:block}

/* ---------- links & type ---------- */
a{color:var(--brand);text-decoration:none}
a:hover{text-decoration:underline;text-underline-offset:3px}
h1,h2,h3,h4,h5,h6{font-family:var(--f-display);color:var(--ink);line-height:1.14;letter-spacing:-.01em;margin:.2em 0 .5em;font-weight:600}
h1{font-size:clamp(1.72rem,4.6vw,2.55rem);font-weight:700}
h2{font-size:clamp(1.34rem,3.2vw,1.85rem)}
h3{font-size:clamp(1.12rem,2.2vw,1.32rem)}
h4{font-size:1.05rem}
p{margin:0 0 1rem}
strong{font-weight:600}
small{font-size:.82rem}
.eyebrow{font-family:var(--f-mono);font-size:.72rem;letter-spacing:.16em;text-transform:uppercase;color:var(--brand);font-weight:600;margin:0 0 .55rem}
.lead{font-size:clamp(1.02rem,2vw,1.16rem);color:var(--ink-2)}
.muted{color:var(--muted)}
.center{text-align:center}

/* ---------- header ---------- */
.site-header{position:sticky;top:0;z-index:50;background:rgba(255,255,255,.92);backdrop-filter:blur(8px);border-bottom:1px solid var(--line)}
.nav{display:flex;align-items:center;gap:1rem;min-height:62px}
.brand{display:flex;align-items:center;gap:.6rem;font-family:var(--f-display);font-weight:700;color:var(--ink);font-size:1.06rem;letter-spacing:-.02em}
.brand:hover{text-decoration:none}
.brand .glyph{width:30px;height:30px;flex:none;display:grid;place-items:center;border:1.5px solid var(--ink);border-radius:7px;background:var(--surface)}
.brand .glyph svg{display:block}
.nav-spacer{flex:1}
.nav-links{display:flex;align-items:center;gap:.15rem;list-style:none;margin:0;padding:0}
.nav-links a{color:var(--ink-2);font-size:.93rem;padding:.5rem .7rem;border-radius:8px;font-weight:500}
.nav-links a:hover{background:var(--surface-2);text-decoration:none;color:var(--ink)}
.nav-toggle{display:none;appearance:none;border:1px solid var(--line);background:var(--surface);border-radius:8px;width:42px;height:38px;cursor:pointer}
.nav-toggle span,.nav-toggle span::before,.nav-toggle span::after{content:"";display:block;width:18px;height:2px;background:var(--ink);margin:0 auto;position:relative;transition:.2s}
.nav-toggle span::before{position:absolute;top:-6px}
.nav-toggle span::after{position:absolute;top:6px}
@media (max-width:860px){
  .nav-toggle{display:block}
  .nav-links{position:absolute;left:0;right:0;top:100%;flex-direction:column;align-items:stretch;gap:0;background:var(--surface);border-bottom:1px solid var(--line);padding:.4rem;box-shadow:var(--shadow);display:none}
  .nav-links.open{display:flex}
  .nav-links a{padding:.75rem .8rem;border-radius:8px}
}

/* ---------- hero ---------- */
.hero{position:relative;overflow:hidden;background:
   linear-gradient(180deg,#fff, #fff 40%, var(--paper));
  border-bottom:1px solid var(--line)}
.hero::before{ /* blueprint grid */
  content:"";position:absolute;inset:0;pointer-events:none;opacity:.5;
  background-image:linear-gradient(var(--line-2) 1px,transparent 1px),linear-gradient(90deg,var(--line-2) 1px,transparent 1px);
  background-size:26px 26px;
  -webkit-mask-image:radial-gradient(120% 90% at 70% 0,#000,transparent 72%);
          mask-image:radial-gradient(120% 90% at 70% 0,#000,transparent 72%);
}
.hero .wrap{position:relative}
.hero-head{max-width:44rem;padding-top:clamp(1.5rem,4vw,2.5rem)}
.hero-head h1{margin-bottom:.5rem}
.hero-sub{color:var(--ink-2);font-size:clamp(1rem,2vw,1.14rem);margin-bottom:.25rem;max-width:40rem}

/* ---------- calculator shell ---------- */
.calc{background:var(--surface);border:1px solid var(--line);border-radius:16px;box-shadow:var(--shadow);overflow:hidden;margin-top:clamp(1.25rem,3vw,1.75rem)}
.calc-tabs{display:flex;gap:2px;overflow-x:auto;background:var(--surface-2);border-bottom:1px solid var(--line);scrollbar-width:none}
.calc-tabs::-webkit-scrollbar{display:none}
.calc-tab{appearance:none;border:0;background:transparent;font-family:var(--f-body);font-weight:500;font-size:.9rem;color:var(--muted);padding:.8rem 1rem;white-space:nowrap;cursor:pointer;border-bottom:2px solid transparent}
.calc-tab[aria-selected="true"]{color:var(--ink);background:var(--surface);border-bottom-color:var(--brand)}
.calc-tab:hover{color:var(--ink)}
.calc-body{display:grid;grid-template-columns:1fr;gap:0}
@media (min-width:900px){.calc-body{grid-template-columns:1.05fr .95fr}}

.calc-inputs{padding:clamp(1.1rem,3vw,1.6rem)}
.calc-output{padding:clamp(1.1rem,3vw,1.6rem);background:linear-gradient(180deg,#0b1f33,#0e2740);color:#eaf1f7;border-top:1px solid var(--line)}
@media (min-width:900px){.calc-output{border-top:0;border-left:1px solid var(--line)}}

.field{margin-bottom:1rem}
.field > label{display:block;font-weight:600;font-size:.9rem;margin-bottom:.35rem;color:var(--ink)}
.field .hint{font-size:.78rem;color:var(--muted);margin-top:.3rem}
.control{display:flex;gap:.5rem}
.control input[type=number],.control select,.input{
  width:100%;font-family:var(--f-mono);font-size:1rem;color:var(--ink);
  background:var(--surface);border:1.5px solid var(--line);border-radius:10px;
  padding:.7rem .8rem;transition:border-color .15s,box-shadow .15s;min-width:0;
}
.control select,select.unit{font-family:var(--f-body)}
.unit{flex:0 0 6.2rem}
input[type=number]:focus,select:focus,.input:focus{outline:none;border-color:var(--brand);box-shadow:0 0 0 3px var(--brand-tint)}
input[type=number].err{border-color:var(--bad);box-shadow:0 0 0 3px var(--bad-tint)}
.field-err{color:var(--bad);font-size:.8rem;margin-top:.35rem;display:none}
.field-err.show{display:block}

/* segmented control (radius/diameter/circumference) */
.seg{display:inline-flex;background:var(--surface-2);border:1px solid var(--line);border-radius:10px;padding:3px;gap:2px}
.seg button{appearance:none;border:0;background:transparent;font-family:var(--f-body);font-size:.85rem;font-weight:500;color:var(--muted);padding:.4rem .7rem;border-radius:7px;cursor:pointer}
.seg button[aria-pressed="true"]{background:var(--surface);color:var(--ink);box-shadow:var(--shadow-sm)}

.btn-row{display:flex;gap:.6rem;flex-wrap:wrap;margin-top:.4rem}
.btn{appearance:none;cursor:pointer;font-family:var(--f-body);font-weight:600;font-size:.95rem;border-radius:10px;padding:.72rem 1.15rem;border:1.5px solid transparent;transition:.15s;display:inline-flex;align-items:center;gap:.45rem}
.btn-primary{background:var(--brand);color:#fff}
.btn-primary:hover{background:var(--brand-strong);text-decoration:none}
.btn-primary:active{transform:translateY(1px)}
.btn-ghost{background:var(--surface);color:var(--ink);border-color:var(--line)}
.btn-ghost:hover{background:var(--surface-2);text-decoration:none}
.btn:focus-visible{outline:3px solid var(--brand-tint);outline-offset:2px}
.btn-block{width:100%;justify-content:center}

/* output / readout */
.readout-label{font-family:var(--f-mono);font-size:.72rem;letter-spacing:.14em;text-transform:uppercase;color:#7fb3bb;margin:0 0 .35rem}
.readout{font-family:var(--f-mono);font-weight:600;line-height:1.1;color:var(--accent);font-size:clamp(1.7rem,6vw,2.5rem);word-break:break-word}
.readout .u{color:#cfe0ea;font-size:.5em;font-weight:500;margin-left:.15em}
.readout-exact{font-family:var(--f-mono);color:#cfe0ea;font-size:.95rem;margin-top:.3rem}
.readout-note{color:#a9c2d1;font-size:.82rem;margin-top:.5rem}
.eq-grid{margin-top:1.1rem;border-top:1px solid rgba(255,255,255,.12);padding-top:.9rem}
.eq-grid h4{color:#eaf1f7;font-size:.82rem;letter-spacing:.06em;text-transform:uppercase;margin:0 0 .55rem;font-family:var(--f-mono);font-weight:500}
.eq-row{display:flex;justify-content:space-between;gap:1rem;padding:.32rem 0;border-bottom:1px dashed rgba(255,255,255,.1);font-size:.92rem}
.eq-row:last-child{border-bottom:0}
.eq-row .k{color:#a9c2d1}
.eq-row .v{font-family:var(--f-mono);color:#eaf1f7;text-align:right}
.out-actions{display:flex;gap:.5rem;flex-wrap:wrap;margin-top:1rem}
.out-actions button{appearance:none;cursor:pointer;font-family:var(--f-body);font-size:.84rem;font-weight:500;color:#eaf1f7;background:rgba(255,255,255,.08);border:1px solid rgba(255,255,255,.18);border-radius:8px;padding:.45rem .7rem;transition:.15s}
.out-actions button:hover{background:rgba(255,255,255,.16)}
.copied{color:#8ee6b0!important}

.fill-wrap{margin-top:.9rem}
.fill-bar{height:12px;background:rgba(255,255,255,.12);border-radius:99px;overflow:hidden}
.fill-bar > i{display:block;height:100%;background:linear-gradient(90deg,#0e7c86,#39c0cc);border-radius:99px;transition:width .35s}
.fill-meta{display:flex;justify-content:space-between;font-size:.8rem;color:#a9c2d1;margin-top:.35rem;font-family:var(--f-mono)}

/* mobile: jump-to-result affordance */
.jump-result{display:none}
@media (max-width:899px){
  .jump-result{display:inline-flex}
}

/* ---------- diagram ---------- */
.diagram{background:var(--surface-2);border:1px solid var(--line);border-radius:12px;padding:1rem;margin-top:1rem}
.diagram svg{width:100%;height:auto;display:block}
.diagram-cap{font-size:.8rem;color:var(--muted);margin-top:.5rem;font-family:var(--f-mono)}

/* ---------- generic cards / grids ---------- */
.card{background:var(--surface);border:1px solid var(--line);border-radius:var(--r);padding:clamp(1rem,3vw,1.5rem);box-shadow:var(--shadow-sm)}
.grid{display:grid;gap:var(--gap)}
.grid-2{grid-template-columns:1fr}
.grid-3{grid-template-columns:1fr}
@media (min-width:720px){.grid-2{grid-template-columns:1fr 1fr}.grid-3{grid-template-columns:1fr 1fr}}
@media (min-width:960px){.grid-3{grid-template-columns:repeat(3,1fr)}}

.prose{max-width:46rem}
.prose h2{margin-top:1.9rem}
.prose h3{margin-top:1.4rem}
.prose ul,.prose ol{padding-left:1.2rem;margin:0 0 1rem}
.prose li{margin-bottom:.4rem}
.prose code{font-family:var(--f-mono);background:var(--surface-2);border:1px solid var(--line);border-radius:6px;padding:.05rem .35rem;font-size:.9em}
.formula{font-family:var(--f-mono);background:var(--ink);color:#eaf1f7;border-radius:10px;padding:.85rem 1rem;display:block;overflow-x:auto;margin:.6rem 0 1rem;font-size:.98rem}
.formula .hl{color:#39c0cc}

/* callout */
.note{border-left:3px solid var(--brand);background:var(--brand-tint);border-radius:0 10px 10px 0;padding:.85rem 1rem;margin:1rem 0}
.note.warn{border-color:var(--accent);background:var(--accent-tint)}
.note p:last-child{margin-bottom:0}

/* table */
.table-wrap{overflow-x:auto;border:1px solid var(--line);border-radius:12px;margin:1rem 0}
table.data{width:100%;border-collapse:collapse;font-size:.92rem;min-width:460px}
table.data th,table.data td{text-align:left;padding:.7rem .9rem;border-bottom:1px solid var(--line-2)}
table.data thead th{background:var(--surface-2);font-family:var(--f-display);font-weight:600;font-size:.85rem;letter-spacing:.02em;position:sticky;top:0}
table.data td:not(:first-child){font-family:var(--f-mono)}
table.data tr:last-child td{border-bottom:0}

/* steps */
.steps{counter-reset:s;list-style:none;padding:0;margin:1rem 0}
.steps li{position:relative;padding-left:2.6rem;margin-bottom:.9rem}
.steps li::before{counter-increment:s;content:counter(s);position:absolute;left:0;top:-2px;width:1.85rem;height:1.85rem;background:var(--brand-tint);color:var(--brand-strong);border-radius:8px;display:grid;place-items:center;font-family:var(--f-mono);font-weight:600;font-size:.9rem}

/* FAQ */
.faq details{border:1px solid var(--line);border-radius:10px;background:var(--surface);margin-bottom:.6rem;overflow:hidden}
.faq summary{cursor:pointer;padding:.9rem 1.1rem;font-weight:600;font-family:var(--f-display);list-style:none;display:flex;justify-content:space-between;align-items:center;gap:1rem}
.faq summary::-webkit-details-marker{display:none}
.faq summary::after{content:"+";font-family:var(--f-mono);color:var(--brand);font-size:1.2rem;transition:.2s}
.faq details[open] summary::after{transform:rotate(45deg)}
.faq .faq-a{padding:0 1.1rem 1rem;color:var(--ink-2)}

/* related / tag cards */
.rel-grid{display:grid;gap:.7rem;grid-template-columns:1fr}
@media (min-width:640px){.rel-grid{grid-template-columns:1fr 1fr}}
@media (min-width:980px){.rel-grid{grid-template-columns:1fr 1fr 1fr}}
.rel-card{display:block;border:1px solid var(--line);border-radius:10px;padding:.85rem 1rem;background:var(--surface);transition:.15s}
.rel-card:hover{border-color:var(--brand);box-shadow:var(--shadow-sm);text-decoration:none;transform:translateY(-1px)}
.rel-card .rc-t{font-family:var(--f-display);font-weight:600;color:var(--ink);font-size:.98rem;display:block;margin-bottom:.15rem}
.rel-card .rc-d{color:var(--muted);font-size:.82rem}

.chips{display:flex;flex-wrap:wrap;gap:.45rem;margin:.5rem 0}
.chip{display:inline-block;font-size:.82rem;color:var(--brand-strong);background:var(--brand-tint);border:1px solid #cfe6e7;border-radius:99px;padding:.28rem .7rem}
.chip:hover{text-decoration:none;background:#d5ecec}

/* breadcrumb */
.crumbs{font-size:.82rem;color:var(--muted);padding:.9rem 0 0;font-family:var(--f-mono)}
.crumbs a{color:var(--muted)}
.crumbs a:hover{color:var(--brand)}
.crumbs span{margin:0 .35rem}

/* history */
.history{margin-top:1rem}
.history ul{list-style:none;padding:0;margin:.5rem 0 0}
.history li{display:flex;justify-content:space-between;gap:1rem;padding:.5rem .7rem;border:1px solid var(--line);border-radius:8px;margin-bottom:.4rem;font-size:.86rem;background:var(--surface)}
.history .h-v{font-family:var(--f-mono);color:var(--ink)}
.history-clear{font-size:.8rem;color:var(--muted);background:none;border:0;cursor:pointer;text-decoration:underline}

/* ad slots */
.ad-slot{margin:1.5rem auto;max-width:100%;min-height:90px;display:flex;align-items:center;justify-content:center;color:var(--muted);font-size:.75rem;font-family:var(--f-mono);border:1px dashed var(--line);border-radius:10px;background:repeating-linear-gradient(45deg,#fff,#fff 10px,var(--surface-2) 10px,var(--surface-2) 20px)}
.ad-slot::before{content:"Advertisement"}
.ad-slot[data-filled] {border:0;background:none}
.ad-slot[data-filled]::before{content:""}

/* ---------- footer ---------- */
.site-footer{background:var(--ink);color:#c7d5e2;margin-top:2rem}
.site-footer a{color:#c7d5e2}
.site-footer a:hover{color:#fff}
.foot-top{display:grid;gap:2rem;grid-template-columns:1fr;padding-block:clamp(2rem,5vw,3rem)}
@media (min-width:720px){.foot-top{grid-template-columns:1.4fr 1fr 1fr}}
@media (min-width:980px){.foot-top{grid-template-columns:1.6fr 1fr 1fr 1fr}}
.foot-brand .brand{color:#fff}
.foot-brand .glyph{border-color:#fff}
.foot-brand p{color:#9fb3c4;font-size:.9rem;max-width:22rem}
.foot-col h4{color:#fff;font-size:.82rem;letter-spacing:.06em;text-transform:uppercase;font-family:var(--f-mono);font-weight:500;margin:0 0 .8rem}
.foot-col ul{list-style:none;padding:0;margin:0}
.foot-col li{margin-bottom:.5rem;font-size:.9rem}
.foot-bottom{border-top:1px solid rgba(255,255,255,.12);padding-block:1.1rem;display:flex;flex-wrap:wrap;gap:.6rem 1.5rem;justify-content:space-between;align-items:center;font-size:.82rem;color:#9fb3c4}
.foot-bottom .partners{display:flex;gap:1rem;flex-wrap:wrap}

/* cookie banner */
.cookie{position:fixed;left:1rem;right:1rem;bottom:1rem;z-index:80;background:var(--ink);color:#eaf1f7;border-radius:12px;box-shadow:0 10px 40px rgba(0,0,0,.3);padding:1rem 1.15rem;display:none;gap:1rem;align-items:center;flex-wrap:wrap;max-width:640px;margin-inline:auto}
.cookie.show{display:flex}
.cookie p{margin:0;font-size:.86rem;flex:1 1 16rem;color:#c7d5e2}
.cookie a{color:#7fd0d8}
.cookie .btn{padding:.5rem .95rem;font-size:.86rem}

/* 404 */
.err-hero{text-align:center;padding-block:clamp(3rem,10vw,6rem)}
.err-code{font-family:var(--f-mono);font-size:clamp(3.5rem,14vw,6rem);color:var(--brand);font-weight:600;line-height:1}

/* utilities */
.stack>*+*{margin-top:1rem}
.hr{height:1px;background:var(--line);border:0;margin:2rem 0}
.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}
.tag-list{columns:2 220px;gap:1.5rem}
.tag-list a{display:block;padding:.25rem 0;font-size:.92rem}
:focus-visible{outline:3px solid var(--brand-tint);outline-offset:2px}

/* testimonials */
.quote-grid{display:grid;gap:var(--gap);grid-template-columns:1fr;margin:1rem 0}
@media (min-width:760px){.quote-grid{grid-template-columns:repeat(3,1fr)}}
.quote{margin:0;background:var(--surface);border:1px solid var(--line);border-left:3px solid var(--brand);border-radius:0 12px 12px 0;padding:1.1rem 1.2rem;box-shadow:var(--shadow-sm)}
.quote blockquote{margin:0 0 .6rem;font-size:.98rem;color:var(--ink-2);line-height:1.55}
.quote figcaption{font-family:var(--f-mono);font-size:.78rem;letter-spacing:.04em;color:var(--muted)}

/* ============================================================
   Language switcher (multi-locale) — added for i18n
   ============================================================ */
.lang-switch{position:relative;margin-left:.5rem}
.lang-switch>summary{
  list-style:none;cursor:pointer;display:inline-flex;align-items:center;gap:.4rem;
  padding:.4rem .6rem;border:1px solid var(--line);border-radius:var(--r-sm);
  background:var(--surface);color:var(--ink);font-family:var(--f-body);
  font-size:.85rem;font-weight:600;line-height:1;white-space:nowrap}
.lang-switch>summary::-webkit-details-marker{display:none}
.lang-switch>summary svg{color:var(--muted);flex:0 0 auto}
.lang-switch>summary:hover{border-color:var(--brand);color:var(--brand)}
.lang-switch[open]>summary{border-color:var(--brand);color:var(--brand)}
.lang-switch>ul{
  position:absolute;right:0;top:calc(100% + .35rem);z-index:60;margin:0;padding:.3rem;
  list-style:none;min-width:11rem;background:var(--surface);
  border:1px solid var(--line);border-radius:var(--r-sm);box-shadow:var(--shadow)}
.lang-switch>ul li{margin:0}
.lang-switch>ul a{
  display:block;padding:.5rem .6rem;border-radius:6px;color:var(--ink-2);
  text-decoration:none;font-size:.9rem;font-weight:500;white-space:nowrap}
.lang-switch>ul a:hover{background:var(--surface-2);color:var(--brand)}
.lang-switch>ul a[aria-current="true"]{color:var(--brand);font-weight:700;background:var(--brand-tint)}
@media (max-width:560px){
  .lang-switch>summary span{display:none}      /* icon-only on small screens */
  .lang-switch>summary{padding:.45rem}
}