[hidden] { display: none !important; }
/* X20 «Vetro su tinta», amber tint (kit ~/kit-x20/vetro). One typeface: Schibsted Grotesk, self-hosted (OFL, fonts/OFL.txt). */
@font-face { font-family: "Schibsted Grotesk"; src: url("/fonts/SchibstedGrotesk-VF.woff2") format("woff2"); font-weight: 400 900; font-style: normal; font-display: swap; }
:root {
  --tint-rgb: 183, 121, 31;
  --base: #fff9f0;
  --glass: rgba(255, 255, 255, .66);
  --glass-strong: rgba(255, 255, 255, .8);
  --glass-edge: rgba(255, 255, 255, .95);
  --glass-edge-low: rgba(150, 120, 80, .22);
  --shadow: 0 1px 2px rgba(60, 40, 10, .06), 0 10px 26px rgba(60, 40, 10, .07), 0 30px 64px rgba(60, 40, 10, .07);
  --surface: #fffdf9;
  --sunk: rgba(183, 121, 31, .07);
  --text: #0e1a33;
  --muted: #4d5568;
  --line: rgba(14, 26, 51, .13);
  --accent: #8a5410;
  --accent-fill: #b7791f;
  --accent-soft: #fbefd9;
  --c1: #9a5a08;   /* plate curves */
  --c2: #2c5d8f;   /* AC load line, series 2 */
  --c3: #2f7445;   /* DC load line, series 3 */
  --c4: #8a2f6b;   /* series 4 */
  --grid: rgba(14, 26, 51, .09);
  --warn: #a12d0b;
  --warn-bg: #fdeee6;
  --ok: #17603a;
  --focus: #0e1a33;
  --radius: 14px;
  --radius-lg: 20px;
  --sans: "Schibsted Grotesk", sans-serif;
  color-scheme: light;
}
:root[data-theme="dark"] {
  --base: #15120e;
  --glass: rgba(40, 34, 27, .62);
  --glass-strong: rgba(46, 39, 31, .82);
  --glass-edge: rgba(255, 235, 200, .13);
  --glass-edge-low: rgba(0, 0, 0, .35);
  --shadow: 0 1px 2px rgba(0, 0, 0, .3), 0 10px 26px rgba(0, 0, 0, .28), 0 30px 64px rgba(0, 0, 0, .3);
  --surface: #221d17;
  --sunk: rgba(240, 180, 90, .07);
  --text: #f1ebe1;
  --muted: #b7ad9e;
  --line: rgba(255, 240, 215, .14);
  --accent: #f2b467;
  --accent-fill: #d99a45;
  --accent-soft: #3b2c18;
  --c1: #f2b467;
  --c2: #8dbbe8;
  --c3: #95d3a0;
  --c4: #e59acb;
  --grid: rgba(255, 240, 215, .09);
  --warn: #ff9f7a;
  --warn-bg: #3c231a;
  --ok: #95d3a0;
  --focus: #f1ebe1;
  color-scheme: dark;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --base: #15120e; --glass: rgba(40, 34, 27, .62); --glass-strong: rgba(46, 39, 31, .82);
    --glass-edge: rgba(255, 235, 200, .13); --glass-edge-low: rgba(0, 0, 0, .35);
    --shadow: 0 1px 2px rgba(0, 0, 0, .3), 0 10px 26px rgba(0, 0, 0, .28), 0 30px 64px rgba(0, 0, 0, .3);
    --surface: #221d17; --sunk: rgba(240, 180, 90, .07); --text: #f1ebe1; --muted: #b7ad9e;
    --line: rgba(255, 240, 215, .14); --accent: #f2b467; --accent-fill: #d99a45; --accent-soft: #3b2c18;
    --c1: #f2b467; --c2: #8dbbe8; --c3: #95d3a0; --c4: #e59acb; --grid: rgba(255, 240, 215, .09);
    --warn: #ff9f7a; --warn-bg: #3c231a; --ok: #95d3a0; --focus: #f1ebe1; color-scheme: dark;
  }
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; min-height: 100%; background: var(--base); }
body {
  margin: 0; color: var(--text); font: 15px/1.45 var(--sans); isolation: isolate; min-height: 100vh;
  background:
    radial-gradient(ellipse at 10% 0%, rgba(var(--tint-rgb), .045), transparent 55%),
    radial-gradient(ellipse at 95% 40%, rgba(var(--tint-rgb), .04), transparent 60%),
    var(--base);
  background-attachment: fixed;
}
/* glass panels: header, sidebar, schematic and chart plates */
.top, .side, .sch-wrap, .chart, .tube-info {
  background: linear-gradient(150deg, rgba(255, 255, 255, .22), rgba(255, 255, 255, 0) 50%), var(--glass);
  border: 1px solid var(--glass-edge); border-bottom-color: var(--glass-edge-low);
  box-shadow: var(--shadow), inset 0 1px 0 var(--glass-edge);
  -webkit-backdrop-filter: blur(28px) saturate(160%); backdrop-filter: blur(28px) saturate(160%);
}
:root[data-theme="dark"] :is(.top, .side, .sch-wrap, .chart, .tube-info) { background: linear-gradient(150deg, rgba(255, 240, 215, .05), rgba(255, 240, 215, 0) 50%), var(--glass); }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) :is(.top, .side, .sch-wrap, .chart, .tube-info) { background: linear-gradient(150deg, rgba(255, 240, 215, .05), rgba(255, 240, 215, 0) 50%), var(--glass); } }
/* technical grid: 5 mm paper behind schematics and charts */
.sch-wrap, .chart {
  --g: rgba(var(--tint-rgb), .10); --g2: rgba(var(--tint-rgb), .05);
  background-image:
    linear-gradient(var(--g) 1px, transparent 1px), linear-gradient(90deg, var(--g) 1px, transparent 1px),
    linear-gradient(var(--g2) 1px, transparent 1px), linear-gradient(90deg, var(--g2) 1px, transparent 1px),
    linear-gradient(var(--glass), var(--glass));
  background-size: 50px 50px, 50px 50px, 10px 10px, 10px 10px, auto;
}
:root[data-theme="dark"] :is(.sch-wrap, .chart) { --g: rgba(255, 220, 160, .07); --g2: rgba(255, 220, 160, .035); }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) :is(.sch-wrap, .chart) { --g: rgba(255, 220, 160, .07); --g2: rgba(255, 220, 160, .035); } }
* { scrollbar-width: thin; scrollbar-color: rgba(120, 100, 70, .35) transparent; }
*::-webkit-scrollbar { width: 8px; height: 8px; background: transparent; }
*::-webkit-scrollbar-thumb { background: rgba(120, 100, 70, .35); border-radius: 8px; }
.num, td.v, table.data td, input[type="text"] { font-variant-numeric: tabular-nums; }

a { color: var(--accent); text-underline-offset: 3px; }
a:hover { text-decoration-thickness: 2px; }
:focus-visible { outline: 2px solid var(--focus); outline-offset: 2px; border-radius: 4px; }
h1, h2, h3 { line-height: 1.2; font-weight: 650; letter-spacing: 0; }
h1 { font-size: 1.45rem; margin: 0; font-weight: 700; }
h2 { font-size: 1.05rem; margin: 0 0 .5rem; }
h3 { font-size: .98rem; margin: 1rem 0 .4rem; }
p { margin: .4rem 0 .8rem; }
sub { font-size: .75em; }
.muted { color: var(--muted); }

.skip { position: absolute; left: -999px; top: 0; background: var(--surface); padding: .5rem 1rem; z-index: 10; }
.skip:focus { left: .5rem; top: .5rem; }

/* header: brand, the one high-voltage note, switches */
.top { position: sticky; top: 0; z-index: 5; border-radius: 0; border-width: 0 0 1px; }
.bar { display: flex; align-items: center; gap: 1rem; max-width: 1760px; margin: 0 auto; padding: .45rem 1rem; }
.brand { display: inline-flex; align-items: center; gap: .45rem; color: var(--text); text-decoration: none; font-weight: 750; font-size: 1.08rem; flex: none; }
.logo { width: 24px; height: 24px; color: var(--accent); }
.safety { flex: 1; margin: 0; font-size: .82rem; color: var(--text); text-align: center; }
.safety strong { color: var(--warn); font-weight: 700; }
.switches { display: flex; gap: .5rem; align-items: center; flex: none; }
.seg { display: inline-flex; border: 1px solid var(--line); border-radius: 10px; overflow: hidden; background: var(--glass-strong); }
.seg button { background: none; border: 0; color: var(--muted); font: inherit; font-size: .82rem; font-weight: 600; padding: .25rem .6rem; cursor: pointer; min-height: 32px; }
.seg button[aria-pressed="true"] { background: var(--text); color: var(--base); }
.icon-btn { background: var(--glass-strong); border: 1px solid var(--line); border-radius: 10px; color: var(--text); width: 36px; height: 34px; display: inline-grid; place-items: center; cursor: pointer; }
.icon-btn svg { width: 19px; height: 19px; }

/* shell: tool index on the left */
.shell { display: grid; grid-template-columns: 228px minmax(0, 1fr); gap: 1.25rem; max-width: 1760px; margin: 0 auto; padding: 1rem 1rem 0; align-items: start; }
.side { position: sticky; top: 3.6rem; border-radius: var(--radius); padding: .5rem .45rem .7rem; max-height: calc(100vh - 5rem); overflow: auto; }
.nav .grp + .grp { margin-top: .3rem; }
.nav h2 { font-size: .68rem; font-weight: 700; text-transform: uppercase; letter-spacing: .07em; color: var(--muted); margin: .3rem .55rem .1rem; }
.nav ul { list-style: none; margin: 0; padding: 0; }
.nav a { display: block; color: var(--text); text-decoration: none; padding: .14rem .55rem; border-radius: 7px; font-size: .88rem; line-height: 1.35; }
.nav a:hover { background: var(--sunk); }
.nav a[aria-current="page"] { background: var(--accent-soft); color: var(--text); font-weight: 650; box-shadow: inset 0 0 0 1px rgba(var(--tint-rgb), .35); }
.nav-toggle { display: none; }
@media (max-width: 1023px) {
  .shell { grid-template-columns: minmax(0, 1fr); gap: .75rem; padding-top: .6rem; }
  .side { position: static; max-height: none; padding: .35rem; }
  .nav-toggle { display: flex; align-items: center; justify-content: space-between; gap: .5rem; width: 100%; min-height: 40px; padding: .3rem .6rem; font: inherit; font-weight: 650; color: var(--text); background: none; border: 0; cursor: pointer; text-align: left; }
  .nav-toggle .hint { color: var(--muted); font-weight: 500; font-size: .85rem; display: inline-flex; align-items: center; gap: .3rem; white-space: nowrap; }
  .nav-toggle svg { width: 16px; height: 16px; transition: transform .18s cubic-bezier(.2, .8, .2, 1); }
  .nav-toggle[aria-expanded="true"] svg { transform: rotate(180deg); }
  .nav { display: none; grid-template-columns: repeat(auto-fill, minmax(170px, 1fr)); gap: .3rem .8rem; padding: .3rem .2rem .4rem; }
  .nav.open { display: grid; }
  .nav .grp + .grp { margin-top: 0; }
  .nav a { padding: .4rem .55rem; }
}

main { display: block; min-width: 0; padding: 0 0 3rem; outline: none; }
main:focus, main:focus-visible { outline: none; }
.sch-wrap.wide .sch { max-width: min(100%, calc(var(--sch-w, 420px) * 1.35)); }
.sch-wrap.wide { overflow-x: auto; }
@media (max-width: 760px) { .sch-wrap.wide .sch { min-width: 640px; } }

/* tool page */
.tool-head { display: flex; align-items: center; justify-content: space-between; gap: .6rem 1rem; flex-wrap: wrap; margin: .15rem 0 .8rem; }
.tool-actions { display: flex; gap: .4rem; align-items: center; }
.bench { display: grid; grid-template-columns: minmax(0, 1fr); gap: 1.1rem; }
@media (min-width: 1100px) {
  .bench { grid-template-columns: minmax(360px, 5fr) minmax(0, 7fr); }
}
.col-in, .col-out { min-width: 0; }
.sch-wrap { margin: 0 0 .9rem; border-radius: var(--radius); padding: .6rem; }
.sch { display: block; width: 100%; max-width: calc(var(--sch-w, 420px) * 1.25); height: auto; margin: 0 auto; overflow: visible; }

/* schematic symbols */
.sch .w { fill: none; stroke: var(--text); stroke-width: 1.4; stroke-linecap: round; stroke-linejoin: round; }
.sch .sym { fill: none; stroke: var(--text); stroke-width: 1.6; stroke-linejoin: round; stroke-linecap: round; }
.sch .sym.fill { fill: var(--text); }
.sch .sym.grid { stroke-dasharray: 3 2.4; stroke-width: 1.3; }
.sch .env { fill: none; stroke: var(--text); stroke-width: 1.3; }
.sch .dot { fill: var(--text); }
.sch .term { fill: var(--surface); stroke: var(--text); stroke-width: 1.3; }
.sch .hit { fill: transparent; stroke: none; }
.sch text { font-family: var(--sans); font-size: 12.5px; fill: var(--text); }
.sch .lab { font-weight: 650; }
.sch .val { fill: var(--muted); font-size: 12px; }
.sch .tag { font-weight: 700; font-size: 12.5px; }
.sch .pm { font-size: 11px; font-weight: 700; }
.sch .ann { fill: var(--accent); font-weight: 650; font-size: 12.5px; }
.sch .cmp { cursor: pointer; }
.sch .cmp:hover :is(.sym, .env, .w), .sch .cmp.hot :is(.sym, .env, .w) { stroke: var(--accent-fill); stroke-width: 2.2; }
.sch .cmp:hover .sym.fill, .sch .cmp.hot .sym.fill { fill: var(--accent-fill); }
.sch .cmp:hover .lab, .sch .cmp.hot .lab { fill: var(--accent); }

/* inputs */
fieldset { border: 0; margin: 0 0 .5rem; padding: 0; min-width: 0; }
legend { font-size: .7rem; font-weight: 700; text-transform: uppercase; letter-spacing: .07em; color: var(--muted); padding: 0; margin: .5rem 0 .2rem; }
.field { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 10.5rem); align-items: center; gap: .3rem .6rem; padding: .16rem .3rem; margin: 0 -.3rem; border-radius: 8px; }
.field.sel { grid-template-columns: minmax(0, 1fr) minmax(0, 13rem); }
.field.flash { animation: flash 1.1s ease-out; }
@keyframes flash { from { background: var(--accent-soft); } to { background: transparent; } }
.field label, .check label { font-size: .9rem; display: flex; gap: .45rem; align-items: baseline; min-width: 0; }
label .sym, th .sym { font-weight: 700; color: var(--text); white-space: nowrap; }
label .lt { color: var(--muted); }
.field .ctl { display: flex; align-items: center; gap: .35rem; }
.field .unit { color: var(--muted); font-size: .85rem; min-width: 1.4rem; }
.field input[type="text"], .field select {
  width: 100%; min-width: 0; font: inherit; font-size: .93rem; color: var(--text);
  background: var(--glass-strong); border: 1px solid var(--line); border-radius: 8px; padding: .26rem .5rem; min-height: 32px;
}
.field input[type="text"] { text-align: right; }
.field input[aria-invalid="true"] { border-color: var(--warn); background: var(--warn-bg); }
.field input[type="range"] { width: 100%; accent-color: var(--accent-fill); }
.field .hint { grid-column: 1 / -1; font-size: .8rem; color: var(--muted); }
.check { display: flex; gap: .5rem; align-items: center; padding: .2rem 0; }
.check input { accent-color: var(--accent-fill); }

/* results */
table.res { width: 100%; border-collapse: collapse; font-size: .9rem; }
table.res th, table.res td { text-align: left; padding: .26rem .35rem; border-bottom: 1px solid var(--line); vertical-align: baseline; }
table.res th { font-weight: 400; color: var(--muted); overflow-wrap: anywhere; }
table.res th .sym { margin-right: .45rem; }
table.res td.v { white-space: nowrap; text-align: right; color: var(--text); font-weight: 600; }
table.res td.e { width: 1.6rem; text-align: right; padding-left: 0; }
table.res tr.sub th { color: var(--text); font-weight: 700; font-size: .7rem; text-transform: uppercase; letter-spacing: .07em; padding-top: .9rem; border-bottom-color: var(--text); }
table.res tr.warn td, table.res tr.warn th { color: var(--warn); }
.eqref { display: inline-block; min-width: 1.15rem; font-size: .7rem; font-weight: 700; text-align: center; color: var(--muted); border: 1px solid var(--line); border-radius: 5px; text-decoration: none; line-height: 1.35; }
.eqref:hover { color: var(--accent); border-color: var(--accent); }
.flag { display: inline-block; font-size: .7rem; font-weight: 650; padding: .02rem .4rem; border-radius: 100px; margin-left: .4rem; }
.flag.warn { color: var(--warn); background: var(--warn-bg); }
.note { font-size: .84rem; color: var(--muted); }
.alert { border: 1px solid color-mix(in srgb, var(--warn) 35%, transparent); background: var(--warn-bg); color: var(--text); padding: .45rem .75rem; font-size: .88rem; margin: .5rem 0; border-radius: 10px; }

.formulas { margin-top: .9rem; border-top: 1px solid var(--line); padding-top: .3rem; }
.formulas summary, details.pts summary { cursor: pointer; font-size: .88rem; font-weight: 600; color: var(--text); padding: .3rem 0; }
details.pts { margin: .4rem 0; }
.formulas ol { margin: .3rem 0 0; padding-left: 1.4rem; }
.formulas li { margin: .2rem 0; padding: .15rem .3rem; font-size: .88rem; border-radius: 6px; }
.formulas li.flash { animation: flash 1.4s ease-out; }
.formulas .eq { font-size: .98rem; }
.formulas .ref { color: var(--muted); font-size: .8rem; display: block; }

.btn { font: inherit; font-size: .84rem; font-weight: 600; color: var(--text); background: var(--glass-strong); border: 1px solid var(--line); border-radius: 8px; padding: .28rem .7rem; cursor: pointer; min-height: 32px; }
.btn:hover { border-color: var(--text); }
.status { font-size: .84rem; color: var(--ok); }
.actions { display: flex; flex-wrap: wrap; gap: .5rem; margin: .4rem 0; }

/* charts */
.chart { width: 100%; margin: 0 0 .8rem; border-radius: var(--radius); padding: .5rem .6rem .3rem; }
.chart + .chart { margin-top: -.2rem; }
.chart svg { width: 100%; height: auto; display: block; overflow: visible; }
.chart .axis { stroke: var(--text); stroke-width: 1; opacity: .55; }
.chart .gridl { stroke: var(--grid); stroke-width: 1; }
.chart .gridm { stroke: var(--grid); stroke-width: .6; opacity: .55; }
.chart text { fill: var(--muted); font: 11px var(--sans); }
.chart .lbl { fill: var(--text); font-size: 11.5px; font-weight: 600; }
.chart .glab { fill: var(--c1); font-size: 10.5px; font-weight: 600; }
.chart .plab { fill: var(--warn); font-size: 10.5px; font-weight: 600; }
.chart .qlab { fill: var(--text); font-size: 11.5px; font-weight: 700; paint-order: stroke; stroke: var(--surface); stroke-width: 3px; }
.chart .llab { font-size: 10.5px; font-weight: 650; paint-order: stroke; stroke: var(--surface); stroke-width: 3px; }
.chart .llab.ll2 { fill: var(--c2); }
.chart .llab.ll3 { fill: var(--c3); }
.chart .curve { fill: none; stroke: var(--c1); stroke-width: 1.5; }
.chart .s2 { stroke: var(--c2); }
.chart .s3 { stroke: var(--c3); }
.chart .s4 { stroke: var(--c4); }
.chart .dash { stroke-dasharray: 5 4; }
.chart .pmax { fill: none; stroke: var(--warn); stroke-width: 1.3; stroke-dasharray: 2 3; }
.chart .guide { fill: none; stroke: var(--text); stroke-width: .9; stroke-dasharray: 3 3; opacity: .6; }
.chart .qpt { fill: var(--accent-fill); stroke: var(--surface); stroke-width: 1.5; }
.chart .dpt { fill: none; stroke: var(--text); stroke-width: 1.1; opacity: .75; }
.legend { display: flex; flex-wrap: wrap; gap: .3rem 1rem; font-size: .8rem; color: var(--muted); margin: .25rem 0 .2rem; padding: 0; list-style: none; }
.legend li { display: inline-flex; align-items: center; gap: .35rem; }
.legend .sw { width: 18px; height: 0; border-top: 2px solid; display: inline-block; }
.legend .sw.dash { border-top-style: dashed; }
.legend .sw.dot { border-top-style: dotted; }
.legend .pt { width: 8px; height: 8px; border-radius: 50%; border: 1.5px solid var(--text); display: inline-block; }

.tube-info { border-radius: var(--radius); padding: .8rem .9rem; margin-top: 1rem; }
.tube-info h2 { font-size: .95rem; margin-top: .4rem; }

/* tables */
.tbl-wrap { overflow-x: auto; }
table.data { border-collapse: collapse; font-size: .84rem; width: 100%; }
table.data th, table.data td { padding: .24rem .5rem; border-bottom: 1px solid var(--line); text-align: right; white-space: nowrap; }
table.data th:first-child, table.data td:first-child { text-align: left; }
table.data thead th { color: var(--muted); font-weight: 600; }
table.data td.txt { text-align: left; font-variant-numeric: normal; }
table.data td.bad { color: var(--warn); font-weight: 650; }

/* resistor body (colour code) */
.resistor { display: flex; align-items: center; justify-content: center; margin: .6rem 0; }
.resistor .body { display: flex; gap: 10px; align-items: stretch; height: 36px; padding: 0 22px; background: #d8c6a3; border-radius: 16px; border: 1px solid #a8956f; }
.resistor .lead-w { width: 40px; height: 2px; background: var(--muted); }
.resistor .band { width: 9px; border-left: 1px solid rgba(0,0,0,.15); border-right: 1px solid rgba(0,0,0,.15); }
.resistor .band.gap { margin-left: 10px; }

/* reference pages */
.prose { max-width: 78ch; }
.prose h1 { margin-bottom: .8rem; }
.prose h2 { margin-top: 1.4rem; }
.prose .tbl-wrap { max-width: none; }
.prose li { margin: .25rem 0; }
.wide { max-width: none; }
.res-list { list-style: none; padding: 0; margin: 0; }
.res-list li { padding: .5rem 0; border-bottom: 1px solid var(--line); display: grid; grid-template-columns: minmax(0, 15rem) minmax(0, 1fr); gap: .2rem 1rem; }
.res-list li a { font-weight: 600; }
.res-list li span { color: var(--muted); font-size: .9rem; }
@media (max-width: 640px) { .res-list li { grid-template-columns: 1fr; } }

.foot { color: var(--muted); font-size: .82rem; }
.foot .wrap { max-width: 1760px; margin: 0 auto; padding: 1rem; display: flex; flex-wrap: wrap; gap: .4rem 1.5rem; justify-content: space-between; border-top: 1px solid var(--line); }

@media (max-width: 760px) {
  .bar { flex-wrap: wrap; gap: .35rem .75rem; padding: .4rem .75rem; }
  .safety { order: 3; flex-basis: 100%; text-align: left; font-size: .78rem; }
  .switches { margin-left: auto; }
  .shell { padding: .5rem .6rem 0; }
}
@media (max-width: 480px) {
  .sch-wrap { overflow-x: auto; }
  .sch { min-width: min(calc(var(--sch-w, 420px) * .85), 560px); }
  .field, .field.sel { grid-template-columns: minmax(0, 1fr) minmax(0, 8.6rem); }
  .field.sel { grid-template-columns: minmax(0, 1fr); gap: .15rem; }
  .sch-wrap { padding: .35rem; }
  .chart { padding: .35rem .3rem .2rem; }
  .tool-head h1 { font-size: 1.25rem; }
}
@media (prefers-reduced-motion: reduce) { *, *::before, *::after { transition: none !important; animation: none !important; } }
@media print {
  .top, .side, .foot, .tool-actions { display: none; }
  .shell { display: block; }
  body { background: #fff; color: #000; }
}
/* one column: schematic, inputs, results, then the reference box */
@media (max-width: 1099px) {
  .col-in { display: contents; }
  .col-in > .sch-wrap { order: 1; }
  .col-in > .inputs { order: 2; }
  .bench > .col-out { order: 3; }
  .col-in > .aside { order: 4; }
}