/* Ekspress hisob — a numbered flow in one column. Layers: fonts, tokens, base, head, hero,
   flow (step rail), builder and legs, result (equation line, receipt), steps and notes,
   charts, tables, foot, narrow. Light throughout: no dark panels. */

@font-face { font-family: "Rubik"; src: url("fonts/rubik.woff2") format("woff2"); font-weight: 300 900; font-display: swap; }
@font-face { font-family: "Literata"; src: url("fonts/literata.woff2") format("woff2"); font-weight: 200 900; font-display: swap; }
@font-face { font-family: "Literata"; src: url("fonts/literata-italic.woff2") format("woff2"); font-weight: 200 900; font-style: italic; font-display: swap; }

:root {
  --chalk: #f6f3ea;
  --paper: #fffdf8;
  --line: #e2dccb;
  --ink: #221d3a;
  --ink-soft: #5a5572;
  --indigo: #2b2350;
  --indigo-tint: #ebe8f6;
  --saffron: #e6a13a;
  --saffron-tint: #fbefd9;
  --saffron-ink: #8f5a07;
  --rose: #b3261e;

  --sans: "Rubik", "Segoe UI", Arial, sans-serif;
  --serif: "Literata", Georgia, serif;
  --gap: clamp(1rem, 0.6rem + 1.6vw, 2rem);
  --col: 46rem;
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--chalk); color: var(--ink); font: 400 1.0625rem/1.7 var(--serif); overflow-wrap: break-word; }
h1, h2, h3, legend, label, .kicker, .brand, .links, .menu, button, .step-n, .eq, .receipt, th { font-family: var(--sans); }
h1, h2, h3 { line-height: 1.15; margin: 0; color: var(--indigo); }
p, ul, ol, dl, figure, fieldset { margin: 0; }
a { color: var(--saffron-ink); text-decoration-thickness: 1px; text-underline-offset: 0.2em; }
@media (hover: hover) and (pointer: fine) { a:hover { color: var(--indigo); text-decoration-thickness: 2px; } }
:focus-visible { outline: 3px solid var(--indigo); outline-offset: 2px; border-radius: 3px; }
.vh { position: absolute; width: 1px; height: 1px; overflow: hidden; clip-path: inset(50%); white-space: nowrap; }
.nowrap { white-space: nowrap; }
.skip { position: absolute; inset-inline-start: 1rem; inset-block-start: -3rem; background: var(--indigo); color: #fff; padding: 0.5rem 0.9rem; z-index: 5; }
.skip:focus { inset-block-start: 1rem; }

/* Head: light, with an indigo rule */
.head { background: var(--chalk); border-block-end: 3px solid var(--indigo); }
.head-inner { max-width: 72rem; margin-inline: auto; padding: 0.8rem var(--gap); display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 0.6rem 2rem; }
.brand { display: flex; align-items: center; gap: 0.6rem; color: var(--indigo); text-decoration: none; }
.brand-x { display: grid; place-items: center; inline-size: 2.1rem; block-size: 2.1rem; border-radius: 50%; background: var(--saffron); color: var(--indigo); font: 700 1.45rem/1 var(--sans); }
.brand-name { font-weight: 700; font-size: 1.25rem; }
.links ul { list-style: none; padding: 0; display: flex; flex-wrap: wrap; gap: 0.15rem 0.35rem; }
.links a { display: inline-block; padding: 0.3rem 0.6rem; border-radius: 0.4rem; color: var(--indigo); text-decoration: none; font-weight: 500; font-size: 0.97rem; }
.links a[aria-current="page"] { background: var(--indigo); color: #fff; }
@media (hover: hover) and (pointer: fine) { .links a:not([aria-current]):hover { background: var(--indigo-tint); } }
.menu { display: none; }
.menu summary { list-style: none; cursor: pointer; font-weight: 600; padding: 0.55rem 0.9rem; border: 2px solid var(--indigo); border-radius: 0.5rem; color: var(--indigo); }
.menu summary::-webkit-details-marker { display: none; }
.menu summary::after { content: " ▾"; }
.menu[open] summary::after { content: " ▴"; }
.menu .links ul { flex-direction: column; gap: 0; padding-block-start: 0.5rem; }
.menu .links a { display: block; padding-block: 0.6rem; border-block-end: 1px solid var(--line); border-radius: 0; font-size: 1.05rem; }

/* Hero */
.hero { max-width: calc(var(--col) + 6rem); margin-inline: auto; padding: clamp(1.75rem, 1rem + 3vw, 3.5rem) var(--gap) 0.5rem calc(var(--gap) + 5rem); }
.kicker { font-weight: 600; font-size: 0.85rem; letter-spacing: 0.1em; text-transform: uppercase; color: var(--saffron-ink); margin-block-end: 0.5rem; }
.hero h1 { font-size: clamp(2rem, 1.3rem + 3vw, 3.3rem); font-weight: 700; }
.lede { font-size: 1.15rem; color: var(--ink-soft); margin-block-start: 0.9rem; max-inline-size: 40rem; }

/* Flow: a numbered rail beside one column */
.flow { max-width: calc(var(--col) + 6rem); margin-inline: auto; padding: 1rem var(--gap) 3rem; }
.step { display: grid; grid-template-columns: 4rem minmax(0, 1fr); column-gap: 1rem; padding-block: 1.75rem; border-block-start: 1px solid var(--line); }
.step:first-child { border-block-start: 0; }
.step-n { font: 800 2.4rem/1 var(--sans); color: var(--saffron); letter-spacing: -0.03em; }
.step-b > * + * { margin-block-start: 0.9rem; }
.step-b h2 { font-size: clamp(1.35rem, 1.15rem + 0.8vw, 1.75rem); font-weight: 700; }
.step-b h3 { font-size: 1.12rem; font-weight: 600; margin-block-start: 1.3rem; }
.step-b h3 + p { margin-block-start: 0.35rem; }
.sub { color: var(--ink-soft); }

/* Builder and legs */
.builder { display: grid; gap: 1.1rem; }
.builder.grid2 { grid-template-columns: repeat(auto-fit, minmax(min(100%, 15rem), 1fr)); gap: 1rem 1.5rem; }
.builder.grid2 .nojs { grid-column: 1 / -1; }
.field label, .leg label, legend { display: block; font-weight: 600; font-size: 0.98rem; color: var(--indigo); }
.legs { border: 0; padding: 0; display: grid; gap: 0.6rem; }
legend { font-size: 1.05rem; margin-block-end: 0.25rem; }
.input-row { display: flex; align-items: stretch; margin-block-start: 0.3rem; border: 1.5px solid var(--indigo); border-radius: 0.55rem; background: var(--paper); overflow: clip; }
.input-row input { flex: 1; inline-size: 0; min-inline-size: 0; border: 0; padding: 0.55rem 0.75rem; font: 500 1.15rem/1.2 var(--sans); font-variant-numeric: tabular-nums; color: var(--ink); background: transparent; }
.input-row input:focus-visible { outline: none; }
.input-row:focus-within { outline: 3px solid var(--indigo); outline-offset: 2px; }
.input-row:has(input[aria-invalid="true"]) { border-color: var(--rose); border-width: 2.5px; }
.input-row input:disabled { color: var(--ink); opacity: 1; -webkit-text-fill-color: var(--ink); }
.unit { display: grid; place-items: center; padding-inline: 0.75rem; background: var(--indigo-tint); font: 500 0.95rem/1 var(--sans); color: var(--indigo); }
.times { display: grid; place-items: center; min-inline-size: 2.1rem; font: 600 1.2rem/1 var(--sans); color: var(--saffron-ink); background: var(--saffron-tint); }
.times:empty { background: transparent; min-inline-size: 0.6rem; }
.hint { display: block; font-size: 0.9rem; color: var(--ink-soft); margin-block-start: 0.3rem; }
.err { display: block; margin-block-start: 0.3rem; font: 600 0.9rem/1.4 var(--sans); color: var(--rose); }
.err::before { content: "⚠ "; }
.err[hidden], .leg[hidden] { display: none; }
.leg { display: grid; grid-template-columns: minmax(0, 13rem) minmax(0, 1fr); column-gap: 1rem; align-items: end; padding: 0.55rem 0.7rem; background: var(--paper); border: 1px solid var(--line); border-radius: 0.7rem; }
.leg label { grid-column: 1 / -1; }
.leg .input-row { margin-block-start: 0.25rem; }
.leg .err { grid-column: 1 / -1; }
.leg-run { display: grid; gap: 0.25rem; padding-block-end: 0.3rem; font: 500 0.95rem/1.2 var(--sans); font-variant-numeric: tabular-nums; color: var(--indigo); }
.leg-bar { block-size: 0.55rem; background: var(--indigo-tint); border-radius: 1rem; overflow: clip; }
.leg-bar span { display: block; block-size: 100%; background: var(--saffron); border-radius: 1rem; }
.leg-tools { display: flex; flex-wrap: wrap; gap: 0.5rem; margin-block-start: 0.3rem; }
.leg-tools button { font: 600 0.95rem/1 var(--sans); padding: 0.65rem 0.95rem; border-radius: 0.5rem; border: 2px solid var(--indigo); background: var(--paper); color: var(--indigo); cursor: pointer; }
.leg-tools button[data-add] { background: var(--indigo); color: #fff; }
.leg-tools button:disabled { opacity: 0.45; cursor: not-allowed; }
.nojs { font-size: 0.92rem; padding: 0.6rem 0.75rem; background: var(--saffron-tint); border-radius: 0.5rem; }

/* Result: an equation line and a receipt */
.result { display: grid; gap: 1rem; }
.eq { font: 600 clamp(1.35rem, 1.05rem + 1.5vw, 2rem)/1.3 var(--sans); color: var(--indigo); font-variant-numeric: tabular-nums; overflow-wrap: anywhere; padding: 0.7rem 0.9rem; background: var(--paper); border: 1px dashed var(--indigo); border-radius: 0.6rem; }
.receipt { display: grid; gap: 0.2rem; }
.line { display: flex; flex-wrap: wrap; align-items: baseline; gap: 0.2rem 0.6rem; padding-block: 0.45rem; border-block-end: 1px dotted var(--line); }
.line dt { flex: 1 1 14rem; color: var(--ink-soft); font-size: 1rem; }
.line dd { margin: 0; font: 600 1.25rem/1.2 var(--sans); font-variant-numeric: tabular-nums; color: var(--indigo); overflow-wrap: anywhere; }
.line.strong { padding: 0.7rem 0.8rem; margin-block: 0.3rem; background: var(--saffron-tint); border: 0; border-radius: 0.6rem; }
.line.strong dt { color: var(--ink); font-weight: 500; }
.line.strong dd { font-size: clamp(1.8rem, 1.4rem + 1.8vw, 2.5rem); color: var(--saffron-ink); }
.invalid { color: var(--rose); font: 600 1rem/1.4 var(--sans); }

/* Calculation steps, further reading */
.calc-steps { padding-inline-start: 1.4rem; display: grid; gap: 0.45rem; font-variant-numeric: tabular-nums; }
.calc-steps li::marker { font: 700 0.95em var(--sans); color: var(--saffron-ink); }
.further { list-style: none; padding: 0; display: grid; gap: 0.55rem; }
.further li { padding-inline-start: 1.1rem; position: relative; }
.further li::before { content: "→"; position: absolute; inset-inline-start: 0; color: var(--saffron-ink); font-family: var(--sans); }
.further a { font: 600 1.05rem/1.4 var(--sans); }

/* Charts and tables */
.fig { background: var(--paper); border: 1px solid var(--line); border-radius: 0.8rem; padding: 0.9rem 1rem; max-inline-size: 32rem; }
.fig figcaption { font-size: 0.92rem; color: var(--ink-soft); margin-block-start: 0.5rem; }
.chart { display: block; inline-size: 100%; block-size: auto; }
.chart .axis { stroke: var(--ink); stroke-width: 1.5; }
.chart .bar { fill: var(--indigo); }
.chart .bar.warm { fill: var(--saffron); }
.chart .bl { font: 500 20px var(--sans); fill: var(--ink); }
.chart .bv { font: 600 19px var(--sans); fill: var(--saffron-ink); }
.chart .halo { paint-order: stroke; stroke: var(--paper); stroke-width: 5px; stroke-linejoin: round; }
.chart .box { fill: #fff; stroke: var(--ink); stroke-width: 1.5; }
.chart .big { font: 700 22px var(--sans); fill: var(--ink); }
.chart .op { font: 600 22px var(--sans); fill: var(--ink-soft); }
.chart .strike { stroke: var(--rose); stroke-width: 3.5; stroke-linecap: round; }
.chart .mark { font: 600 18px var(--sans); fill: var(--rose); }
.tbl-wrap { position: relative; overflow-x: auto; background: var(--paper); border: 1px solid var(--line); border-radius: 0.8rem; }
.plain { border-collapse: collapse; inline-size: 100%; font: 400 0.98rem/1.4 var(--sans); font-variant-numeric: tabular-nums; }
.plain th, .plain td { padding: 0.55rem 0.85rem; text-align: end; border-block-end: 1px solid var(--line); white-space: nowrap; }
.plain thead th { font-size: 0.85rem; color: var(--ink-soft); vertical-align: bottom; white-space: normal; overflow-wrap: normal; min-inline-size: 5.5rem; }
.plain tbody th { text-align: start; }
.cap { font-size: 0.9rem; color: var(--ink-soft); margin-block-start: 0.5rem; }
.formulas { display: grid; gap: 0.6rem; }
.formulas div { display: grid; grid-template-columns: minmax(0, 15rem) minmax(0, 1fr); gap: 0.2rem 1rem; padding: 0.6rem 0.8rem; background: var(--paper); border: 1px solid var(--line); border-radius: 0.6rem; }
.formulas dt { font: 600 1rem/1.4 var(--sans); color: var(--indigo); }
.formulas dd { margin: 0; }
.step-b ul:not(.further) { padding-inline-start: 1.2rem; display: grid; gap: 0.35rem; }

/* Foot: light, with a rule */
.foot { border-block-start: 3px solid var(--indigo); background: var(--paper); }
.foot-inner { max-width: calc(var(--col) + 6rem); margin-inline: auto; padding: 1.5rem var(--gap) 2rem; display: grid; gap: 0.55rem; font-size: 0.95rem; color: var(--ink-soft); }
.foot-links { list-style: none; padding: 0; display: flex; flex-wrap: wrap; gap: 0.3rem 1.2rem; font-family: var(--sans); }

@media (max-width: 47.99rem) {
  .wide-nav { display: none; }
  .menu { display: block; flex-basis: 100%; }
  .hero { padding-inline-start: var(--gap); }
  .step { grid-template-columns: minmax(0, 1fr); }
  .step-n { font-size: 1.6rem; margin-block-end: 0.3rem; }
  .leg { grid-template-columns: minmax(0, 1fr); row-gap: 0.4rem; }
  .formulas div { grid-template-columns: 1fr; }
}