/* ============================================================
   Design tokens
   ============================================================ */
:root{
  --ink:        #1B2A4A;
  --ink-soft:   #2E3F63;
  --paper:      #FAF8F3;
  --paper-dim:  #F1ECE0;
  --gold:       #B08D3E;
  --gold-soft:  #D8C48F;
  --slate:      #5A6478;
  --pass:       #2F6B4F;
  --pass-bg:    #E6EFE9;
  --fail:       #8A3B2E;
  --fail-bg:    #F4E7E3;
  --line:       #DAD2BE;

  --font-display: 'Amiri', 'Traditional Arabic', serif;
  --font-body:    'Tajawal', 'Segoe UI', sans-serif;

  --radius: 4px;
  --shadow-card: 0 1px 2px rgba(27,42,74,0.06), 0 8px 24px -12px rgba(27,42,74,0.18);
}

*{ box-sizing: border-box; }

html{ scroll-behavior: smooth; }

body{
  margin: 0;
  min-height: 100vh;
  background: var(--paper);
  font-family: var(--font-body);
  color: var(--ink);
  position: relative;
  overflow-x: hidden;
}

/* faint radial watermark, evokes an official seal without being literal */
.seal-bg{
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  background:
    radial-gradient(circle at 50% 8%, rgba(176,141,62,0.07), transparent 42%),
    repeating-linear-gradient(135deg, rgba(27,42,74,0.015) 0px, rgba(27,42,74,0.015) 1px, transparent 1px, transparent 26px);
}

.page{
  position: relative;
  z-index: 1;
  max-width: 760px;
  margin: 0 auto;
  padding: 48px 24px 64px;
}

/* ============================================================
   Letterhead
   ============================================================ */
.letterhead{
  text-align: center;
  margin-bottom: 36px;
}

.letterhead-line{
  height: 2px;
  margin: 14px auto;
  max-width: 220px;
  background: linear-gradient(90deg, transparent, var(--gold), transparent);
}

.eyebrow{
  margin: 0;
  font-size: 12.5px;
  letter-spacing: 0.04em;
  color: var(--slate);
  font-weight: 700;
  text-transform: none;
}

.letterhead h1{
  font-family: var(--font-display);
  font-weight: 700;
  font-size: clamp(28px, 5vw, 38px);
  margin: 10px 0 6px;
  color: var(--ink);
}

.subtitle{
  margin: 0;
  font-size: 14.5px;
  color: var(--slate);
  font-weight: 400;
}

/* ============================================================
   Disclaimer banner
   ============================================================ */
.disclaimer{
  background: var(--paper-dim);
  border: 1px solid var(--gold-soft);
  border-inline-start: 4px solid var(--gold);
  border-radius: 2px;
  padding: 14px 18px;
  margin: 0 0 24px;
}

.disclaimer p{
  margin: 0;
  font-size: 12.5px;
  line-height: 1.85;
  color: var(--ink-soft);
}

.disclaimer p + p{
  margin-top: 8px;
  color: var(--slate);
}

.disclaimer strong{
  color: var(--fail);
}

.disclaimer a{
  color: var(--ink);
  font-weight: 700;
  text-decoration: underline;
  text-decoration-color: var(--gold);
  text-underline-offset: 2px;
}

.disclaimer a:hover{ color: var(--gold); }

/* ============================================================
   Mode switch
   ============================================================ */
.mode-switch{
  display: flex;
  gap: 8px;
  background: var(--paper-dim);
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 4px;
  margin: 0 auto 24px;
  max-width: 460px;
}

.mode-btn{
  flex: 1;
  border: none;
  background: transparent;
  font-family: var(--font-body);
  font-size: 14px;
  font-weight: 700;
  color: var(--slate);
  padding: 10px 14px;
  border-radius: 999px;
  cursor: pointer;
  transition: background 0.2s ease, color 0.2s ease, box-shadow 0.2s ease;
}

.mode-btn:hover{ color: var(--ink); }

.mode-btn.is-active{
  background: var(--ink);
  color: var(--paper);
  box-shadow: 0 4px 14px -6px rgba(27,42,74,0.5);
}

.mode-btn:focus-visible,
input:focus-visible{
  outline: 2px solid var(--gold);
  outline-offset: 2px;
}

/* ============================================================
   Card
   ============================================================ */
.card{
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow-card);
  padding: 32px;
  position: relative;
}

.card::before{
  content: "";
  position: absolute;
  top: 0; right: 0; left: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--ink) 0%, var(--gold) 50%, var(--ink) 100%);
  border-radius: var(--radius) var(--radius) 0 0;
}

.panel-intro{
  font-size: 15px;
  line-height: 1.9;
  color: var(--ink-soft);
  background: var(--paper-dim);
  border-inline-start: 3px solid var(--gold);
  padding: 14px 16px;
  border-radius: 2px;
  margin: 0 0 24px;
}

.panel-intro strong{ color: var(--ink); }

/* ============================================================
   Fields
   ============================================================ */
.field-grid{
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px 18px;
}

.field-grid-single{
  grid-template-columns: 1fr;
}

.field{ display: flex; flex-direction: column; }

.field-pair{
  grid-column: 1 / -1;
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: end;
  gap: 10px;
}

.pair-divider{
  padding-bottom: 12px;
  font-size: 13px;
  color: var(--slate);
  white-space: nowrap;
}

label{
  font-size: 13.5px;
  font-weight: 700;
  color: var(--ink-soft);
  margin-bottom: 7px;
}

.hint{
  font-weight: 400;
  color: var(--slate);
  font-size: 12.5px;
}

input[type="number"]{
  font-family: var(--font-body);
  font-size: 16px;
  font-weight: 500;
  color: var(--ink);
  background: var(--paper);
  border: 1.5px solid var(--line);
  border-radius: var(--radius);
  padding: 11px 13px;
  transition: border-color 0.15s ease, background 0.15s ease;
  width: 100%;
}

input[type="number"]:hover{ border-color: var(--gold-soft); }

input[type="number"]:focus{
  border-color: var(--gold);
  background: #fff;
}

input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button{
  opacity: 0.5;
}

.field-note{
  margin: 6px 2px 0;
  font-size: 12px;
  color: var(--slate);
}

/* ============================================================
   Status line (pass/fail threshold banner)
   ============================================================ */
.status-line{
  margin-top: 18px;
  min-height: 0;
  font-size: 13.5px;
  font-weight: 700;
  border-radius: var(--radius);
  transition: all 0.25s ease;
  overflow: hidden;
}

.status-line.show{
  padding: 10px 14px;
  margin-top: 18px;
}

.status-line.pass{
  background: var(--pass-bg);
  color: var(--pass);
  border: 1px solid #BEDACB;
}

.status-line.fail{
  background: var(--fail-bg);
  color: var(--fail);
  border: 1px solid #E4C4BB;
}

/* ============================================================
   Ledger — the signature element: the equation fills in live
   ============================================================ */
.ledger{
  margin-top: 28px;
  border-top: 1px dashed var(--line);
  padding-top: 22px;
}

.ledger-title{
  font-family: var(--font-display);
  font-size: 15px;
  font-weight: 700;
  color: var(--ink);
  margin: 0 0 14px;
}

.ledger-row{
  display: grid;
  grid-template-columns: 1fr auto auto;
  align-items: baseline;
  gap: 10px;
  padding: 9px 0;
  border-bottom: 1px solid #F0ECE1;
  font-size: 13.5px;
}

.ledger-row.ledger-sub{
  color: var(--slate);
  font-size: 12.5px;
  padding-inline-start: 14px;
}

.ledger-row.ledger-sub .ledger-label::before{
  content: "↳ ";
  color: var(--gold);
}

.ledger-label{ color: var(--ink-soft); }
.ledger-label em{ font-style: normal; color: var(--slate); font-size: 0.92em; }

.ledger-expr{
  font-variant-numeric: tabular-nums;
  color: var(--slate);
  font-size: 12.5px;
  white-space: nowrap;
  direction: ltr;
  unicode-bidi: isolate;
}

.ledger-val{
  font-variant-numeric: tabular-nums;
  font-weight: 700;
  color: var(--ink);
  min-width: 64px;
  text-align: left;
  direction: ltr;
}

.ledger-row.ledger-final{
  border-bottom: none;
  border-top: 2px solid var(--ink);
  margin-top: 6px;
  padding-top: 14px;
}

.ledger-row.ledger-final .ledger-label{
  font-family: var(--font-display);
  font-size: 16px;
  font-weight: 700;
  color: var(--ink);
}

.ledger-row.ledger-final .ledger-val{
  font-size: 22px;
  color: var(--gold);
  min-width: 90px;
}

/* ============================================================
   Reference block — official source image
   ============================================================ */
.reference-block{
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow-card);
  margin: 24px 0;
  overflow: hidden;
}

.reference-block summary{
  cursor: pointer;
  list-style: none;
  padding: 14px 20px;
  font-family: var(--font-display);
  font-size: 14.5px;
  font-weight: 700;
  color: var(--ink);
  background: var(--paper-dim);
  border-bottom: 1px solid var(--line);
  display: flex;
  align-items: center;
  gap: 8px;
  user-select: none;
}

.reference-block summary::-webkit-details-marker{ display: none; }

.reference-block summary::before{
  content: "▸";
  color: var(--gold);
  font-size: 12px;
  transition: transform 0.2s ease;
}

.reference-block[open] summary::before{
  transform: rotate(90deg);
}

.reference-block summary:hover{ color: var(--gold); }

.reference-block figure{
  margin: 0;
  padding: 20px;
}

.reference-block img{
  width: 100%;
  height: auto;
  display: block;
  border: 1px solid var(--line);
  border-radius: 2px;
}

.reference-block figcaption{
  margin-top: 12px;
  font-size: 12px;
  color: var(--slate);
  line-height: 1.7;
  text-align: center;
}

/* ============================================================
   Footer
   ============================================================ */
.page-footer{
  text-align: center;
  margin-top: 32px;
}

.page-footer p{
  font-size: 12px;
  color: var(--slate);
  line-height: 1.7;
}

.page-footer p + p{
  margin-top: 8px;
}

.page-footer .footer-note{
  font-size: 11.5px;
}

.page-footer .footer-credit{
  font-size: 11.5px;
  color: var(--ink-soft);
  font-weight: 700;
}

.page-footer a{
  color: var(--ink-soft);
  font-weight: 700;
  text-decoration: underline;
  text-decoration-color: var(--gold-soft);
  text-underline-offset: 2px;
}

.page-footer a:hover{ color: var(--gold); }

/* ============================================================
   Responsive
   ============================================================ */
@media (max-width: 560px){
  .page{ padding: 32px 16px 48px; }
  .card{ padding: 22px; }
  .field-grid{ grid-template-columns: 1fr; }
  .field-pair{ grid-template-columns: 1fr; }
  .pair-divider{ padding-bottom: 0; text-align: center; }
  .ledger-row{
    grid-template-columns: 1fr;
    gap: 2px;
  }
  .ledger-expr, .ledger-val{ text-align: right; direction: rtl; }
  .ledger-val{ font-size: 15px; }
  .ledger-row.ledger-final .ledger-val{ font-size: 22px; }
}

/* Reduced motion */
@media (prefers-reduced-motion: reduce){
  html{ scroll-behavior: auto; }
  *{ transition: none !important; }
}