/*
  Naruhodo Tutoring — Calculator Shared Stylesheet
  Ocean theme: matches wireframe-calculator-template.html
  Applied by all /calc/*.html pages via <link rel="stylesheet" href="/calc/shared.css">
*/

/* ═══════════════════════════════
   TOKENS
═══════════════════════════════ */
:root {
  --ocean-abyss:  #050d18;
  --ocean-deep:   #0a1628;
  --ocean-dark:   #0d2137;
  --ocean-mid:    #134b6e;
  --ocean-light:  #1e7898;
  --ocean-bright: #38b6d4;
  --ocean-foam:   #7dd8e8;
  --ocean-pale:   #b8eef7;
  --sand-dark:    #1a2a3a;
  --sand-mid:     #243447;
  --sand-warm:    #2d3e50;
  --coral-soft:   #ffa07a;
  --pearl:        #e8f4f8;
  --text-light:   #c5dce6;
  --text-muted:   #8aa4b5;

  --grad-ocean:   linear-gradient(135deg,#050d18 0%,#0a1628 25%,#0d2137 50%,#134b6e 75%,#1e7898 100%);
  --grad-surface: linear-gradient(180deg,#38b6d4 0%,#1e7898 100%);
  --grad-card:    linear-gradient(145deg,rgba(20,40,60,.85) 0%,rgba(13,33,55,.95) 100%);

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --radius-pill: 50px;

  --shadow-card: 0 4px 24px rgba(0,0,0,.4);
  --shadow-btn:  0 4px 20px rgba(56,182,212,.2);
}

/* ═══════════════════════════════
   BASE RESET
═══════════════════════════════ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  font-family: 'Outfit', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--ocean-dark);
  color: var(--text-light);
  line-height: 1.6;
  min-height: 100vh;
}

h1, h2, h3, h4, h5 {
  font-family: 'DM Serif Display', Georgia, serif;
  line-height: 1.2;
}

a { color: var(--ocean-foam); text-decoration: none; }
a:hover { color: var(--pearl); text-decoration: underline; }

/* ═══════════════════════════════
   ZONE 1 — NAV
═══════════════════════════════ */
.calc-nav {
  background: rgba(10,22,40,.92);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  padding: 14px 32px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid rgba(56,182,212,.15);
  position: sticky;
  top: 0;
  z-index: 200;
}

.calc-nav-left { display: flex; align-items: center; gap: 10px; }

.calc-nav-logo {
  width: 32px; height: 32px;
  background: var(--grad-surface);
  border-radius: 50%;
  border: 1.5px solid rgba(125,216,232,.4);
  flex-shrink: 0;
  display: flex; align-items: center; justify-content: center;
  overflow: hidden;
}
.calc-nav-logo img { width: 100%; height: 100%; object-fit: cover; }

.calc-breadcrumb {
  display: flex; align-items: center; gap: 6px;
  font-size: 12px; color: var(--text-muted);
}
.calc-breadcrumb a { color: var(--ocean-foam); }
.calc-breadcrumb a:hover { color: var(--pearl); text-decoration: none; }
.calc-breadcrumb .sep { color: var(--ocean-mid); }
.calc-breadcrumb .cur { color: var(--pearl); font-weight: 600; }

.calc-nav-book {
  background: var(--grad-surface);
  color: var(--pearl);
  border-radius: var(--radius-pill);
  padding: 8px 18px;
  font-size: 11px;
  font-weight: 700;
  white-space: nowrap;
  transition: opacity .15s;
}
.calc-nav-book:hover { opacity: .85; color: var(--pearl); text-decoration: none; }

/* ═══════════════════════════════
   ZONE 2 — TOOL HEADER
═══════════════════════════════ */
.calc-header {
  background: var(--grad-ocean);
  padding: 32px 32px 24px;
  border-bottom: 1px solid rgba(56,182,212,.15);
  position: relative;
  overflow: hidden;
}
.calc-header::after {
  content: '';
  position: absolute;
  inset: 0;
  background: radial-gradient(ellipse 60% 80% at 0% 50%, rgba(56,182,212,.05), transparent);
  pointer-events: none;
}
.calc-header-inner {
  max-width: 960px;
  margin: 0 auto;
  position: relative;
  z-index: 1;
}

/* Badges */
.calc-badges { display: flex; gap: 8px; margin-bottom: 14px; flex-wrap: wrap; }
.calc-badge {
  display: inline-block;
  font-size: 10px; font-weight: 700;
  padding: 3px 12px;
  border-radius: var(--radius-pill);
  text-transform: uppercase;
  letter-spacing: .05em;
}
.cb-subject  { background: rgba(56,182,212,.18); color: var(--ocean-foam); border: 1px solid rgba(56,182,212,.3); }
.cb-basic    { background: rgba(50,200,120,.15); color: #6de8a8; border: 1px solid rgba(50,200,120,.3); }
.cb-inter    { background: rgba(56,182,212,.15); color: var(--ocean-foam); border: 1px solid rgba(56,182,212,.25); }
.cb-advanced { background: rgba(160,100,240,.15); color: #c8a0f8; border: 1px solid rgba(160,100,240,.25); }
.cb-applied  { background: rgba(240,170,60,.15); color: #f0c870; border: 1px solid rgba(240,170,60,.25); }
.cb-cs       { background: rgba(0,212,255,.12); color: #7de8ff; border: 1px solid rgba(0,212,255,.25); }

.calc-header h1 {
  font-size: clamp(1.5rem, 3vw, 2.2rem);
  color: var(--pearl);
  margin-bottom: 8px;
}
.calc-header-desc {
  font-size: 14px;
  color: var(--text-light);
  max-width: 640px;
  line-height: 1.65;
  margin-bottom: 16px;
}

.calc-header-meta {
  display: flex; gap: 20px; flex-wrap: wrap;
  padding-top: 16px;
  border-top: 1px solid rgba(56,182,212,.12);
}
.calc-meta-item {
  font-size: 11px; color: var(--text-muted);
  display: flex; align-items: center; gap: 6px;
}
.calc-meta-dot {
  width: 6px; height: 6px;
  background: var(--ocean-bright);
  border-radius: 50%;
  flex-shrink: 0;
}
.calc-meta-dot.green { background: #2ea86a; }

/* ═══════════════════════════════
   ZONE 3 — WORKSPACE
═══════════════════════════════ */
.calc-workspace {
  background: var(--ocean-dark);
  padding: 24px 32px;
}
.calc-workspace-inner {
  max-width: 960px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 18px;
}
.calc-workspace-inner.single-col {
  grid-template-columns: 1fr;
  max-width: 640px;
}
.calc-workspace-inner.wide-right {
  grid-template-columns: 1fr 1.2fr;
}

/* Input panel */
.calc-input-panel {
  background: var(--grad-card);
  border: 1px solid rgba(56,182,212,.2);
  border-radius: var(--radius-lg);
  padding: 20px;
  border-top: 3px solid var(--ocean-bright);
}
.calc-panel-title {
  font-family: 'Outfit', sans-serif;
  font-size: 11px; font-weight: 700;
  text-transform: uppercase; letter-spacing: .08em;
  color: var(--ocean-bright);
  margin-bottom: 16px;
}

/* Form controls */
.calc-field { margin-bottom: 14px; }
.calc-label {
  display: block;
  font-size: 11px; font-weight: 600;
  color: var(--text-muted);
  margin-bottom: 6px;
  text-transform: uppercase; letter-spacing: .04em;
}
.calc-input,
.calc-select {
  width: 100%;
  height: 40px;
  background: rgba(255,255,255,.04);
  border: 1.5px solid rgba(56,182,212,.2);
  border-radius: var(--radius-sm);
  padding: 0 12px;
  font-family: 'Outfit', sans-serif;
  font-size: 14px;
  color: var(--pearl);
  outline: none;
  transition: border-color .15s, background .15s;
  appearance: none;
  -webkit-appearance: none;
}
.calc-input::placeholder { color: var(--text-muted); }
.calc-input:focus,
.calc-select:focus {
  border-color: var(--ocean-bright);
  background: rgba(56,182,212,.06);
}
.calc-input.error { border-color: #f87171; }

.calc-select {
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='8' viewBox='0 0 12 8'%3E%3Cpath d='M1 1l5 5 5-5' stroke='%2338b6d4' stroke-width='1.5' fill='none' stroke-linecap='round'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 12px center;
  padding-right: 32px;
  cursor: pointer;
}
.calc-select option { background: var(--ocean-dark); color: var(--pearl); }

.calc-helper {
  font-size: 11px; color: var(--text-muted);
  margin-top: 4px; line-height: 1.4;
}
.calc-error-msg {
  font-size: 11px; color: #f87171;
  margin-top: 4px;
  display: none;
}
.calc-error-msg.visible { display: block; }

/* Radio / toggle row */
.calc-radio-group { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 6px; }
.calc-radio-option {
  display: flex; align-items: center; gap: 6px;
  font-size: 12px; color: var(--text-muted);
  cursor: pointer;
  padding: 5px 12px;
  background: rgba(255,255,255,.03);
  border: 1px solid rgba(56,182,212,.2);
  border-radius: var(--radius-pill);
  transition: background .12s, border-color .12s, color .12s;
  user-select: none;
}
.calc-radio-option input[type="radio"] { display: none; }
.calc-radio-option:has(input:checked),
.calc-radio-option.active {
  background: rgba(56,182,212,.15);
  border-color: var(--ocean-bright);
  color: var(--ocean-foam);
}
.calc-radio-option:hover { border-color: rgba(56,182,212,.4); color: var(--text-light); }

/* Matrix grid input */
.calc-matrix-wrap { overflow-x: auto; padding-bottom: 4px; }
.calc-matrix-grid {
  display: inline-grid;
  gap: 6px;
  margin: 8px 0;
}
.calc-matrix-cell {
  width: 56px; height: 38px;
  background: rgba(255,255,255,.04);
  border: 1.5px solid rgba(56,182,212,.2);
  border-radius: var(--radius-sm);
  text-align: center;
  font-family: 'Outfit', sans-serif;
  font-size: 14px;
  color: var(--pearl);
  outline: none;
  transition: border-color .15s;
}
.calc-matrix-cell:focus { border-color: var(--ocean-bright); background: rgba(56,182,212,.06); }
.calc-matrix-cell.pivot { background: rgba(56,182,212,.15); border-color: var(--ocean-bright); color: var(--ocean-foam); }
.calc-matrix-cell.highlighted { background: rgba(46,168,106,.15); border-color: #2ea86a; color: #7de8a8; }

.calc-matrix-bracket {
  font-size: 64px; font-weight: 200;
  color: var(--text-muted); line-height: 1;
  user-select: none; flex-shrink: 0;
}
.calc-matrix-row { display: flex; align-items: center; gap: 6px; }

/* Expression input */
.calc-expr-input {
  width: 100%;
  height: 48px;
  background: rgba(240,170,60,.06);
  border: 1.5px solid rgba(240,170,60,.2);
  border-radius: var(--radius-sm);
  padding: 0 14px;
  font-family: 'Courier New', monospace;
  font-size: 15px;
  color: #f0d080;
  outline: none;
  transition: border-color .15s;
}
.calc-expr-input:focus { border-color: #f0c870; }
.calc-expr-input::placeholder { color: rgba(240,170,60,.35); }

.calc-sym-btns { display: flex; gap: 5px; flex-wrap: wrap; margin-top: 6px; }
.calc-sym-btn {
  padding: 3px 9px;
  background: rgba(240,170,60,.08);
  border: 1px solid rgba(240,170,60,.2);
  border-radius: 4px;
  font-size: 12px; color: #f0c870;
  cursor: pointer; font-family: 'Courier New', monospace;
  transition: background .12s;
}
.calc-sym-btn:hover { background: rgba(240,170,60,.16); }

/* Graph/canvas input area */
.calc-graph-input {
  width: 100%; min-height: 180px;
  background: rgba(124,92,252,.06);
  border: 1.5px dashed rgba(124,92,252,.25);
  border-radius: var(--radius-md);
  display: flex; align-items: center; justify-content: center;
  font-size: 12px; color: rgba(160,120,240,.6);
  font-style: italic; text-align: center;
  padding: 16px;
}

/* Node / edge controls */
.calc-node-controls { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 8px; }
.calc-node-btn {
  padding: 7px 14px;
  background: rgba(124,92,252,.1);
  border: 1px solid rgba(124,92,252,.25);
  border-radius: var(--radius-sm);
  font-size: 12px; color: #c0a0fc;
  cursor: pointer;
  transition: background .12s, border-color .12s;
}
.calc-node-btn:hover { background: rgba(124,92,252,.2); border-color: rgba(124,92,252,.4); }
.calc-node-btn.active { background: rgba(124,92,252,.25); border-color: #c0a0fc; }

/* Buttons */
.calc-btn {
  width: 100%; padding: 13px;
  background: var(--grad-surface);
  border: none; border-radius: var(--radius-md);
  font-family: 'Outfit', sans-serif;
  font-size: 13px; font-weight: 700;
  color: var(--pearl);
  cursor: pointer;
  margin-top: 12px;
  box-shadow: var(--shadow-btn);
  transition: opacity .15s, transform .1s;
}
.calc-btn:hover { opacity: .9; transform: translateY(-1px); }
.calc-btn:active { transform: translateY(0); opacity: 1; }
.calc-btn:disabled { opacity: .45; cursor: not-allowed; transform: none; }
.calc-btn.loading::after {
  content: '';
  display: inline-block;
  width: 12px; height: 12px;
  border: 2px solid rgba(255,255,255,.3);
  border-top-color: #fff;
  border-radius: 50%;
  animation: spin .7s linear infinite;
  margin-left: 8px;
  vertical-align: middle;
}

.calc-clear-btn {
  width: 100%; padding: 9px;
  background: transparent;
  border: 1px solid rgba(56,182,212,.2);
  border-radius: var(--radius-md);
  font-family: 'Outfit', sans-serif;
  font-size: 11px; color: var(--text-muted);
  cursor: pointer; margin-top: 7px;
  transition: border-color .15s, color .15s;
}
.calc-clear-btn:hover { border-color: rgba(56,182,212,.4); color: var(--text-light); }

.calc-example-row { display: flex; gap: 7px; flex-wrap: wrap; margin-top: 7px; }
.calc-example-btn {
  padding: 5px 11px;
  background: rgba(56,182,212,.07);
  border: 1px solid rgba(56,182,212,.15);
  border-radius: 20px;
  font-size: 11px; color: var(--text-muted);
  cursor: pointer;
  transition: background .12s, border-color .12s, color .12s;
}
.calc-example-btn:hover { background: rgba(56,182,212,.13); border-color: rgba(56,182,212,.3); color: var(--ocean-foam); }

/* Size controls (for matrix rows/cols) */
.calc-size-controls { display: flex; align-items: center; gap: 10px; margin-bottom: 10px; flex-wrap: wrap; }
.calc-size-label { font-size: 11px; color: var(--text-muted); }
.calc-size-input {
  width: 50px; height: 32px;
  background: rgba(255,255,255,.04);
  border: 1.5px solid rgba(56,182,212,.2);
  border-radius: var(--radius-sm);
  text-align: center;
  font-family: 'Outfit', sans-serif;
  font-size: 14px; color: var(--pearl);
  outline: none;
}
.calc-size-input:focus { border-color: var(--ocean-bright); }

/* Output panel */
.calc-output-panel {
  background: var(--grad-card);
  border: 1px solid rgba(56,182,212,.15);
  border-radius: var(--radius-lg);
  padding: 20px;
  border-top: 3px solid var(--ocean-light);
  display: flex; flex-direction: column;
}
.calc-panel-title.output { color: var(--ocean-foam); }

/* Answer block */
.calc-answer-block {
  background: rgba(56,182,212,.07);
  border: 1px solid rgba(56,182,212,.2);
  border-radius: var(--radius-md);
  padding: 14px;
  margin-bottom: 14px;
}
.calc-answer-label {
  font-size: 9px; font-weight: 700;
  text-transform: uppercase; letter-spacing: .08em;
  color: var(--ocean-foam); margin-bottom: 8px;
}
.calc-answer-value {
  font-family: 'DM Serif Display', serif;
  font-size: 1.4rem; color: var(--pearl);
  line-height: 1.3;
  word-break: break-all;
}
.calc-answer-sub {
  font-size: 12px; color: var(--text-muted);
  margin-top: 6px;
}

/* Quick stats 3-grid */
.calc-quick-stats {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 8px; margin-bottom: 14px;
}
.calc-qs-cell {
  background: rgba(255,255,255,.03);
  border: 1px solid rgba(56,182,212,.12);
  border-radius: var(--radius-sm);
  padding: 10px 8px;
  text-align: center;
}
.calc-qs-val {
  font-family: 'DM Serif Display', serif;
  font-size: 1.1rem; color: var(--ocean-foam);
  line-height: 1.2; word-break: break-all;
}
.calc-qs-lbl {
  font-size: 9px; color: var(--text-muted);
  text-transform: uppercase; letter-spacing: .05em;
  margin-top: 3px;
}

/* Empty state */
.calc-empty-state {
  background: rgba(255,255,255,.02);
  border: 1.5px dashed rgba(56,182,212,.15);
  border-radius: var(--radius-md);
  padding: 24px;
  text-align: center;
  font-size: 13px; color: var(--ocean-mid);
  font-style: italic;
  margin-bottom: 14px;
  flex: 1;
}

/* Result matrix / table display */
.calc-result-matrix {
  overflow-x: auto;
  margin-bottom: 12px;
}
.calc-result-grid {
  display: inline-grid; gap: 5px;
}
.calc-result-cell {
  min-width: 56px; padding: 4px 8px;
  text-align: center;
  font-family: 'Courier New', monospace;
  font-size: 13px; color: var(--pearl);
  background: rgba(255,255,255,.04);
  border: 1px solid rgba(56,182,212,.15);
  border-radius: 4px;
}
.calc-result-cell.pivot { background: rgba(56,182,212,.15); color: var(--ocean-foam); border-color: rgba(56,182,212,.3); }
.calc-result-cell.final { background: rgba(46,168,106,.15); color: #7de8a8; border-color: rgba(46,168,106,.3); }

/* Result text */
.calc-result-text {
  font-size: 14px; color: var(--text-light);
  line-height: 1.7;
}
.calc-result-text strong { color: var(--ocean-foam); }

/* Action row */
.calc-action-row {
  display: flex; gap: 8px;
  margin-top: auto; padding-top: 14px;
  border-top: 1px solid rgba(56,182,212,.1);
}
.calc-action-btn {
  flex: 1; padding: 7px;
  background: rgba(255,255,255,.04);
  border: 1px solid rgba(56,182,212,.15);
  border-radius: var(--radius-sm);
  font-size: 11px; color: var(--text-muted);
  cursor: pointer; text-align: center;
  transition: background .12s, color .12s, border-color .12s;
}
.calc-action-btn:hover { background: rgba(56,182,212,.08); color: var(--ocean-foam); border-color: rgba(56,182,212,.3); }

/* ═══════════════════════════════
   ZONE 4 — STEPS
═══════════════════════════════ */
.calc-steps {
  background: var(--ocean-deep);
  padding: 24px 32px;
  border-top: 1px solid rgba(56,182,212,.1);
  display: none; /* hidden until first calculation */
}
.calc-steps.visible { display: block; }
.calc-steps-inner { max-width: 960px; margin: 0 auto; }

.calc-steps-header {
  display: flex; justify-content: space-between;
  align-items: center; margin-bottom: 18px;
}
.calc-steps-title {
  font-family: 'DM Serif Display', serif;
  font-size: 1.4rem; color: var(--pearl);
}
.calc-steps-toggle {
  font-size: 11px; color: var(--ocean-foam);
  background: rgba(56,182,212,.1);
  border: 1px solid rgba(56,182,212,.2);
  border-radius: 7px; padding: 5px 12px;
  cursor: pointer;
  transition: background .12s;
  user-select: none;
}
.calc-steps-toggle:hover { background: rgba(56,182,212,.18); }

.calc-steps-body { overflow: hidden; }
.calc-steps-body.collapsed { display: none; }

.calc-step {
  display: flex; gap: 14px;
  margin-bottom: 16px; padding-bottom: 16px;
  border-bottom: 1px solid rgba(56,182,212,.08);
}
.calc-step:last-child { border-bottom: none; margin-bottom: 0; padding-bottom: 0; }

.calc-step-num {
  width: 30px; height: 30px; flex-shrink: 0;
  background: var(--grad-surface);
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  font-family: 'DM Serif Display', serif;
  font-size: 13px; color: var(--pearl);
  box-shadow: 0 3px 12px rgba(56,182,212,.25);
}
.calc-step-num.done { background: linear-gradient(135deg,#2ea86a,#1a7848); }

.calc-step-content { flex: 1; }
.calc-step-op {
  font-size: 11px; font-weight: 700;
  text-transform: uppercase; letter-spacing: .06em;
  color: var(--text-muted); margin-bottom: 5px;
}
.calc-step-math {
  font-family: 'Courier New', monospace;
  font-size: 14px; color: var(--ocean-pale);
  background: rgba(56,182,212,.06);
  border-radius: 5px; padding: 5px 10px;
  margin: 4px 0; display: inline-block;
  word-break: break-all;
}
.calc-step-math.final { background: rgba(46,168,106,.1); color: #7de8a8; }
.calc-step-note {
  font-size: 12px; color: var(--text-muted);
  margin-top: 5px; line-height: 1.5;
}

/* Matrix inside a step */
.calc-step-matrix {
  display: flex; align-items: center; gap: 6px;
  margin: 6px 0; overflow-x: auto;
}

/* ═══════════════════════════════
   ZONE 5 — VISUALIZATION
═══════════════════════════════ */
.calc-viz {
  background: var(--ocean-abyss);
  padding: 24px 32px;
  border-top: 1px solid rgba(56,182,212,.1);
  display: none;
}
.calc-viz.visible { display: block; }
.calc-viz-inner { max-width: 960px; margin: 0 auto; }
.calc-viz-title {
  font-family: 'DM Serif Display', serif;
  font-size: 1.4rem; color: var(--pearl);
  margin-bottom: 14px;
}

.calc-viz-canvas {
  width: 100%; height: 300px;
  background: linear-gradient(180deg,#050d18 0%,#0a1628 100%);
  border: 1px solid rgba(56,182,212,.15);
  border-radius: var(--radius-lg);
  position: relative; overflow: hidden;
}
.calc-viz-canvas::before {
  content: '';
  position: absolute; inset: 0;
  background-image:
    linear-gradient(rgba(56,182,212,.04) 1px, transparent 1px),
    linear-gradient(90deg, rgba(56,182,212,.04) 1px, transparent 1px);
  background-size: 48px 48px;
  pointer-events: none;
}

.calc-viz-controls {
  display: flex; gap: 8px;
  margin-top: 12px; flex-wrap: wrap; align-items: center;
}
.calc-viz-btn {
  padding: 6px 12px;
  background: rgba(56,182,212,.07);
  border: 1px solid rgba(56,182,212,.15);
  border-radius: 7px;
  font-size: 11px; color: var(--text-muted);
  cursor: pointer;
  transition: background .12s, border-color .12s, color .12s;
}
.calc-viz-btn:hover,
.calc-viz-btn.active {
  background: rgba(56,182,212,.15);
  border-color: rgba(56,182,212,.3);
  color: var(--ocean-foam);
}

/* SVG / Canvas element inside viz */
.calc-viz-canvas canvas,
.calc-viz-canvas svg {
  position: absolute; inset: 0;
  width: 100%; height: 100%;
}

/* ═══════════════════════════════
   ZONE 6 — CONCEPT NOTE
═══════════════════════════════ */
.calc-concept {
  background: var(--ocean-dark);
  padding: 24px 32px;
  border-top: 1px solid rgba(56,182,212,.1);
}
.calc-concept-inner {
  max-width: 960px; margin: 0 auto;
  display: grid; grid-template-columns: 1fr 1fr; gap: 18px;
}
.calc-concept-box {
  background: var(--grad-card);
  border: 1px solid rgba(56,182,212,.15);
  border-radius: var(--radius-md);
  padding: 18px;
  border-left: 3px solid var(--ocean-bright);
}
.calc-concept-box.gold { border-left-color: #f0c870; }

.calc-concept-h {
  font-family: 'Outfit', sans-serif;
  font-size: 10px; font-weight: 700;
  text-transform: uppercase; letter-spacing: .06em;
  color: var(--ocean-foam); margin-bottom: 10px;
}
.calc-concept-h.gold { color: #f0c870; }

.calc-formula {
  font-family: 'Courier New', monospace;
  font-size: 14px; color: var(--ocean-pale);
  background: rgba(56,182,212,.08);
  border-radius: 5px; padding: 8px 12px;
  margin-bottom: 10px; display: block;
  word-break: break-all;
}

.calc-concept-text {
  font-size: 13px; color: var(--text-muted);
  line-height: 1.7;
}
.calc-concept-text p { margin-bottom: 8px; }
.calc-concept-text p:last-child { margin-bottom: 0; }

.calc-tip-box {
  background: rgba(56,182,212,.08);
  border: 1px solid rgba(56,182,212,.15);
  border-radius: 7px;
  padding: 9px 12px;
  font-size: 12px; color: var(--ocean-foam);
  margin-top: 10px; font-style: italic;
  line-height: 1.5;
}
.calc-tip-box::before { content: "💡 "; }

.calc-use-list {
  list-style: none; padding: 0;
  font-size: 13px; color: var(--text-muted);
  line-height: 1.9;
}
.calc-use-list li::before {
  content: "• ";
  color: #f0c870;
}

/* ═══════════════════════════════
   ZONE 7 — RELATED
═══════════════════════════════ */
.calc-related {
  background: var(--sand-dark);
  padding: 24px 32px;
  border-top: 1px solid rgba(56,182,212,.1);
}
.calc-related-inner { max-width: 960px; margin: 0 auto; }
.calc-related-title {
  font-family: 'DM Serif Display', serif;
  font-size: 1.3rem; color: var(--pearl);
  margin-bottom: 14px;
}
.calc-related-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 10px;
}
.calc-related-card {
  background: var(--grad-card);
  border: 1px solid rgba(56,182,212,.15);
  border-radius: var(--radius-md);
  padding: 14px;
  transition: border-color .15s;
  text-decoration: none;
  display: block;
}
.calc-related-card:hover { border-color: var(--ocean-bright); text-decoration: none; }
.calc-rc-badge {
  display: inline-block;
  height: 8px; border-radius: 10px;
  background: rgba(56,182,212,.2);
  margin-bottom: 8px;
}
.calc-rc-title {
  font-size: 13px; font-weight: 600;
  color: var(--pearl); margin-bottom: 4px;
  line-height: 1.3;
}
.calc-rc-desc {
  font-size: 11px; color: var(--text-muted);
  line-height: 1.4; margin-bottom: 8px;
}
.calc-rc-arrow {
  font-size: 11px; color: var(--ocean-bright);
}

/* ═══════════════════════════════
   ZONE 8 — TUTOR CTA
═══════════════════════════════ */
.calc-cta {
  background: var(--grad-ocean);
  padding: 32px;
  border-top: 1px solid rgba(56,182,212,.15);
  position: relative; overflow: hidden;
}
.calc-cta::after {
  content: ''; position: absolute; inset: 0;
  background: radial-gradient(ellipse 60% 80% at 100% 50%, rgba(56,182,212,.08), transparent);
  pointer-events: none;
}
.calc-cta-inner {
  max-width: 960px; margin: 0 auto;
  display: flex; align-items: center;
  justify-content: space-between;
  gap: 20px; flex-wrap: wrap;
  position: relative; z-index: 1;
}
.calc-cta h3 {
  font-family: 'DM Serif Display', serif;
  font-size: 1.5rem; color: var(--pearl);
  margin-bottom: 6px;
}
.calc-cta p {
  font-size: 13px; color: var(--text-muted);
  max-width: 400px; line-height: 1.6;
}
.calc-cta-btn {
  background: var(--pearl);
  color: var(--ocean-dark);
  padding: 13px 28px;
  border-radius: var(--radius-pill);
  font-size: 13px; font-weight: 700;
  white-space: nowrap;
  flex-shrink: 0;
  transition: opacity .15s, transform .1s;
  display: inline-block;
}
.calc-cta-btn:hover { opacity: .9; transform: translateY(-1px); color: var(--ocean-dark); text-decoration: none; }

/* ═══════════════════════════════
   FOOTER
═══════════════════════════════ */
.calc-footer {
  background: var(--ocean-abyss);
  padding: 14px 32px;
  border-top: 1px solid rgba(56,182,212,.08);
}
.calc-footer-inner {
  max-width: 960px; margin: 0 auto;
  display: flex; justify-content: space-between;
  align-items: center; flex-wrap: wrap; gap: 10px;
  font-size: 11px; color: var(--ocean-mid);
}
.calc-footer-links { display: flex; gap: 14px; }
.calc-footer-links a { color: var(--ocean-mid); }
.calc-footer-links a:hover { color: var(--ocean-foam); text-decoration: none; }

/* ═══════════════════════════════
   LOADING / ERROR STATES
═══════════════════════════════ */
@keyframes spin {
  to { transform: rotate(360deg); }
}
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to   { opacity: 1; transform: translateY(0); }
}
.calc-fade-in { animation: fadeIn .25s ease; }

.calc-loading-overlay {
  display: flex; align-items: center; justify-content: center;
  gap: 10px; padding: 20px;
  font-size: 12px; color: var(--text-muted);
}
.calc-spinner {
  width: 20px; height: 20px;
  border: 2px solid rgba(56,182,212,.2);
  border-top-color: var(--ocean-bright);
  border-radius: 50%;
  animation: spin .7s linear infinite;
  flex-shrink: 0;
}

/* Inline status badge */
.calc-status-badge {
  display: inline-flex; align-items: center; gap: 5px;
  font-size: 10px; padding: 2px 8px;
  border-radius: 20px;
}
.calc-status-badge.success { background: rgba(46,168,106,.15); color: #7de8a8; border: 1px solid rgba(46,168,106,.25); }
.calc-status-badge.error   { background: rgba(248,113,113,.1);  color: #f87171; border: 1px solid rgba(248,113,113,.2); }

/* Error inline in output */
.calc-error-block {
  background: rgba(248,113,113,.08);
  border: 1px solid rgba(248,113,113,.2);
  border-radius: var(--radius-sm);
  padding: 10px 14px;
  font-size: 12px; color: #f87171;
  margin-bottom: 10px;
}

/* ═══════════════════════════════
   GRAPH / NODE CANVAS (Bellman-Ford, MST, etc.)
═══════════════════════════════ */
.calc-graph-canvas {
  width: 100%; height: 320px;
  background: rgba(10,14,26,.8);
  border: 1px solid rgba(56,182,212,.15);
  border-radius: var(--radius-md);
  position: relative; overflow: hidden;
  cursor: crosshair;
}
.calc-graph-canvas::before {
  content: ''; position: absolute; inset: 0;
  background-image:
    linear-gradient(rgba(56,182,212,.03) 1px, transparent 1px),
    linear-gradient(90deg, rgba(56,182,212,.03) 1px, transparent 1px);
  background-size: 40px 40px;
  pointer-events: none;
}

/* Distance / result table */
.calc-table {
  width: 100%; border-collapse: collapse;
  font-size: 12px; color: var(--text-muted);
  margin-top: 8px;
}
.calc-table th {
  background: rgba(56,182,212,.08);
  color: var(--ocean-foam);
  padding: 6px 10px; text-align: left;
  font-size: 10px; text-transform: uppercase;
  letter-spacing: .05em; border-bottom: 1px solid rgba(56,182,212,.15);
}
.calc-table td {
  padding: 6px 10px;
  border-bottom: 1px solid rgba(56,182,212,.06);
  font-family: 'Courier New', monospace;
}
.calc-table tr:last-child td { border-bottom: none; }
.calc-table td.updated { color: #7de8a8; }
.calc-table td.source  { color: var(--ocean-foam); font-weight: 600; }

/* ═══════════════════════════════
   RESPONSIVE
═══════════════════════════════ */
@media (max-width: 700px) {
  .calc-nav { padding: 12px 16px; }
  .calc-breadcrumb { display: none; }

  .calc-header { padding: 20px 16px 16px; }
  .calc-header h1 { font-size: 1.4rem; }
  .calc-header-meta { gap: 10px; }

  .calc-workspace { padding: 16px; }
  .calc-workspace-inner,
  .calc-workspace-inner.wide-right {
    grid-template-columns: 1fr;
  }

  .calc-concept-inner { grid-template-columns: 1fr; }

  .calc-steps { padding: 16px; }
  .calc-steps-body { /* collapsed on first load — JS toggles */ }

  .calc-viz-canvas { height: 200px; }

  .calc-related { padding: 16px; }
  .calc-related-grid { grid-template-columns: 1fr; }

  .calc-cta { padding: 20px 16px; }
  .calc-cta-inner { flex-direction: column; align-items: flex-start; }
  .calc-cta h3 { font-size: 1.2rem; }

  .calc-footer { padding: 12px 16px; }

  .calc-quick-stats { grid-template-columns: 1fr 1fr; }
}

@media (max-width: 480px) {
  .calc-nav-logo { display: none; }
  .calc-matrix-cell { width: 44px; height: 34px; font-size: 13px; }
  .calc-result-cell { min-width: 44px; font-size: 12px; }
}

/* ═══════════════════════════════
   PRINT
═══════════════════════════════ */
@media print {
  .calc-nav,
  .calc-cta,
  .calc-related,
  .calc-footer { display: none; }
  .calc-steps { display: block !important; }
  body { background: #fff; color: #000; }
}