:root {
  --ink: #101828;
  --ink-soft: #344054;
  --muted: #667085;
  --line: #e3e7ee;
  --paper: #ffffff;
  --card: #ffffff;
  --tint: #f5f7fa;
  --navy: #0f2a43;
  --teal: #0e7490;
  --teal-dark: #0a5a70;
  --amber: #667085;
  --radius: 6px;
  --maxw: 1120px;
  --pad: 56px;
  --accent-stats: #7c3aed;
  --accent-quality: #0e7490;
  --accent-lss: #16a34a;
  --formula-bg: #ecfeff;
  --practice-bg: #ecfdf5;
  --warning-bg: #fffbeb;
  --danger-bg: #fef2f2;
  --info-bg: #eff6ff;
  --warning-line: #f59e0b;
  --danger-line: #dc2626;
  --info-line: #0284c7;
}
@media (max-width: 900px) { :root { --pad: 32px; } }
@media (max-width: 640px) { :root { --pad: 20px; } }
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; background: var(--paper); color: var(--ink); font-family: 'Work Sans', Arial, sans-serif; line-height: 1.5; }
h1, h2, h3 { font-family: 'Source Serif 4', Georgia, serif; font-weight: 600; margin: 0; }
a { color: var(--teal); text-decoration: none; }
a:hover { color: var(--teal-dark); }
a:focus-visible, button:focus-visible, input:focus-visible, select:focus-visible, textarea:focus-visible { outline: 3px solid rgba(14,116,144,.35); outline-offset: 2px; }
img { max-width: 100%; display: block; }
.wrap { max-width: var(--maxw); margin: 0 auto; padding-left: var(--pad); padding-right: var(--pad); }
.eyebrow { font-size: 13px; font-weight: 700; letter-spacing: 0.1em; text-transform: uppercase; color: var(--teal); margin: 0 0 12px; }
.section { padding: 88px 0; }
.section.tint { background: var(--tint); }
.btn { display: inline-block; padding: 14px 26px; border-radius: var(--radius); font-size: 15px; font-weight: 600; text-decoration: none; white-space: nowrap; transition: transform .15s, box-shadow .15s, background .15s; border: none; cursor: pointer; font-family: inherit; }
.btn:hover { transform: translateY(-2px); box-shadow: 0 8px 20px rgba(0,0,0,0.14); }
.btn-teal { background: var(--teal); color: #fff; }
.btn-teal:hover { color: #fff; background: var(--teal-dark); }
.btn-outline { background: transparent; border: 1px solid #cfd4dc; color: var(--ink); }
.btn-outline:hover { color: var(--ink); background: var(--tint); }
.card { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 26px; }
.grid-3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; }
.grid-2 { display: grid; grid-template-columns: repeat(2, 1fr); gap: 20px; }
@media (max-width: 900px) { .grid-3 { grid-template-columns: repeat(2, 1fr); } }
@media (max-width: 640px) { .grid-3, .grid-2 { grid-template-columns: 1fr; } }
header.site { position: sticky; top: 0; z-index: 20; display: flex; align-items: center; justify-content: space-between; padding: 18px 20px; gap: 10px; border-bottom: 1px solid var(--line); background: rgba(255,255,255,0.96); backdrop-filter: blur(8px); }
.brand { display: flex; align-items: center; gap: 10px; flex-shrink: 0; color: var(--ink); }
.brand:hover { color: var(--ink); }
.brand img { height: 32px; width: auto; }
.brand span { font-family: 'Source Serif 4', Georgia, serif; font-size: 17px; font-weight: 600; white-space: nowrap; }
nav.desktop-nav { display: flex; gap: 18px; font-size: 13.5px; font-weight: 600; white-space: nowrap; }
nav.desktop-nav a { padding: 6px 2px; border-bottom: 2px solid transparent; color: var(--ink); }
nav.desktop-nav a:hover, nav.desktop-nav a[aria-current="page"] { border-bottom-color: var(--teal); color: var(--teal-dark); }
.header-cta { flex-shrink: 0; white-space: nowrap; }
.mnav-check { display: none; }
label.mobile-menu-btn { display: none; align-items: center; justify-content: center; width: 36px; height: 36px; border: 1px solid #cfd4dc; border-radius: 4px; background: #fff; cursor: pointer; flex-shrink: 0; }
nav.mobile-nav { display: none; flex-direction: column; border-bottom: 1px solid var(--line); background: #fff; }
nav.mobile-nav a { padding: 14px 20px; font-size: 14.5px; font-weight: 600; border-bottom: 1px solid var(--line); color: var(--ink); }
@media (max-width: 1080px) { nav.desktop-nav { display: none; } label.mobile-menu-btn { display: flex; } .mnav-check:checked ~ nav.mobile-nav { display: flex; } }
footer.site { padding: 56px 0 32px; border-top: 1px solid var(--line); background: var(--navy); color: #cbd5e1; }
footer.site .brand, footer.site .brand span, footer.site h4 { color: #ffffff; }
footer.site .footer-grid a, footer.site p { color: #cbd5e1; }
footer.site .footer-grid a:hover { color: #ffffff; }
.footer-grid { display: grid; grid-template-columns: 1.4fr 1fr 1fr 1fr; gap: 40px; }
@media (max-width: 900px) { .footer-grid { grid-template-columns: 1fr 1fr; } }
@media (max-width: 640px) { .footer-grid { grid-template-columns: 1fr; } }
.footer-grid h4 { font-size: 12.5px; font-weight: 700; letter-spacing: 0.06em; text-transform: uppercase; margin: 0 0 12px; }
.footer-grid a { display: block; font-size: 13.5px; margin-bottom: 8px; }
.footer-bottom { max-width: var(--maxw); margin: 32px auto 0; padding: 20px var(--pad) 0; border-top: 1px solid rgba(255,255,255,.15); display: flex; justify-content: space-between; flex-wrap: wrap; gap: 8px; font-size: 12.5px; color: #94a3b8; }
.footer-bottom a { display: inline; margin-left: 16px; color: #94a3b8; }
.badge-row { display: flex; flex-wrap: wrap; gap: 10px; margin: 16px 0 0; }
.badge { display: inline-flex; align-items: center; gap: 6px; padding: 7px 12px; border-radius: 999px; color: #fff; font-size: 12px; font-weight: 700; letter-spacing: 0.02em; }
.badge-stats { background: var(--accent-stats); }
.badge-quality { background: var(--accent-quality); }
.badge-lss { background: var(--accent-lss); }
.lesson-objectives { list-style: none; padding: 0; margin: 0; }
.lesson-objectives li { position: relative; padding-left: 32px; margin-bottom: 12px; font-size: 15px; line-height: 1.6; color: var(--ink-soft); }
.lesson-objectives li::before { content: "\2713"; position: absolute; left: 0; top: 1px; width: 22px; height: 22px; border-radius: 999px; background: var(--teal); color: #fff; font-size: 12px; font-weight: 800; display: inline-flex; align-items: center; justify-content: center; }
.callout { padding: 18px 20px; border-radius: var(--radius); border: 1px solid var(--line); margin: 20px 0; background: #fff; font-size: 15px; line-height: 1.65; color: var(--ink-soft); }
.callout strong { color: var(--ink); }
.callout-info { background: var(--info-bg); border-left: 5px solid var(--info-line); border-top-color: transparent; border-right-color: transparent; border-bottom-color: transparent; }
.callout-formula { background: var(--formula-bg); border-left: 5px solid var(--teal); border-top-color: transparent; border-right-color: transparent; border-bottom-color: transparent; }
.callout-practice { background: var(--practice-bg); border-left: 5px solid #16a34a; border-top-color: transparent; border-right-color: transparent; border-bottom-color: transparent; }
.callout-warning { background: var(--warning-bg); border-left: 5px solid var(--warning-line); border-top-color: transparent; border-right-color: transparent; border-bottom-color: transparent; }
.callout-danger { background: var(--danger-bg); border-left: 5px solid var(--danger-line); border-top-color: transparent; border-right-color: transparent; border-bottom-color: transparent; }
.example-box { border-radius: 14px; background: #fff; border: 1px solid var(--line); padding: 28px; box-shadow: 0 10px 30px rgba(15,23,42,0.08); }
.step-list { counter-reset: step-counter; list-style: none; padding: 0; margin: 0; }
.step-list li { counter-increment: step-counter; display: grid; grid-template-columns: 36px 1fr; gap: 14px; margin-bottom: 16px; align-items: start; }
.step-list li::before { content: counter(step-counter); width: 30px; height: 30px; border-radius: 50%; background: var(--navy); color: #fff; display: flex; align-items: center; justify-content: center; font-weight: 800; font-size: 13.5px; }
.step-list li div { font-size: 15px; line-height: 1.6; color: var(--ink-soft); }
.step-list li strong { color: var(--ink); }
.quiz { background: #fff; border: 1px solid var(--line); border-radius: 14px; padding: 26px; }

/* Page-specific lesson components */
.lesson-shell { max-width: 760px; margin: 0 auto; }
.lesson-copy { font-size: 15.5px; line-height: 1.72; color: var(--ink-soft); }
.lesson-copy strong { color: var(--ink); }
.jump-nav { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 22px; }
.jump-nav a { border: 1px solid var(--line); background: #fff; color: var(--ink); border-radius: 999px; padding: 8px 12px; font-size: 12.5px; font-weight: 600; }
.jump-nav a:hover { border-color: var(--teal); color: var(--teal-dark); }
.section-title { font-size: 20px; margin: 32px 0 12px; }
.concept-grid { display: grid; grid-template-columns: repeat(2, minmax(0,1fr)); gap: 14px; margin: 18px 0; }
.concept-card { border: 1px solid var(--line); border-radius: 10px; padding: 18px; background: #fff; }
.concept-card h3 { font-size: 16px; margin-bottom: 8px; color: var(--navy); }
.concept-card p { font-size: 14.5px; line-height: 1.6; color: var(--ink-soft); margin: 0; }
@media (max-width: 640px) { .concept-grid { grid-template-columns: 1fr; } }
.rule-banner { display: grid; grid-template-columns: 1fr auto 1fr; align-items: center; gap: 12px; margin: 18px 0; }
.rule-side { text-align: center; padding: 16px; border-radius: 10px; border: 1px solid var(--line); background: #fff; }
.rule-side strong { display: block; color: var(--navy); font-size: 17px; margin-bottom: 4px; }
.rule-arrow { color: var(--teal); font-size: 25px; font-weight: 700; }
@media (max-width: 640px) { .rule-banner { grid-template-columns: 1fr; } .rule-arrow { transform: rotate(90deg); text-align: center; } }
.formula-line { font-family: 'Courier New', monospace; font-size: 15px; color: var(--navy); font-weight: 700; }
.table-wrap { overflow-x: auto; margin: 18px 0; border: 1px solid var(--line); border-radius: 10px; }
table { width: 100%; border-collapse: collapse; font-size: 14px; background: #fff; }
th { background: var(--navy); color: #fff; text-align: left; padding: 12px 14px; }
td { padding: 12px 14px; border-bottom: 1px solid var(--line); vertical-align: top; color: var(--ink-soft); }
tr:last-child td { border-bottom: 0; }
.interactive { border: 2px solid #b9dce4; border-radius: 14px; padding: 24px; background: linear-gradient(180deg,#fff,#f6fbfc); box-shadow: 0 10px 30px rgba(15,23,42,.08); margin: 20px 0; }
.interactive h3 { font-size: 18px; color: var(--navy); margin-bottom: 8px; }
.interactive p { color: var(--ink-soft); font-size: 14.5px; line-height: 1.6; }
.control-grid { display: grid; grid-template-columns: repeat(2,minmax(0,1fr)); gap: 16px; margin: 18px 0; }
@media (max-width: 640px) { .control-grid { grid-template-columns: 1fr; } }
.field-label { display: block; font-size: 13.5px; font-weight: 700; color: var(--navy); margin-bottom: 6px; }
.interactive input, .interactive select { width: 100%; border: 1px solid #cfd4dc; border-radius: 8px; padding: 11px 12px; font: inherit; background: #fff; color: var(--ink); }
.helper { font-size: 12.5px !important; color: var(--muted) !important; margin: 5px 0 0 !important; }
.result-panel { margin-top: 18px; padding: 18px; border-radius: 10px; border: 1px solid var(--line); background: #fff; }
.result-panel.good { border-left: 6px solid #16a34a; }
.result-panel.caution { border-left: 6px solid #f59e0b; }
.result-panel.neutral { border-left: 6px solid #0284c7; }
.result-panel h4 { margin: 0 0 8px; color: var(--navy); font-size: 16px; }
.result-panel p { margin: 6px 0; }
.output-box { background: #0b1f33; color: #e5eef7; border-radius: 10px; padding: 20px; overflow-x: auto; font-family: 'Courier New', monospace; font-size: 13.5px; line-height: 1.65; margin: 18px 0; }
.output-box strong { color: #fff; }
.minitab-steps { display: grid; gap: 12px; margin: 18px 0; }
.minitab-step { display: grid; grid-template-columns: 34px 1fr; gap: 12px; align-items: start; border: 1px solid var(--line); border-radius: 10px; padding: 14px; background: #fff; }
.minitab-step span { width: 28px; height: 28px; border-radius: 50%; background: var(--teal); color: #fff; display: inline-flex; align-items: center; justify-content: center; font-size: 13px; font-weight: 700; }
.minitab-step p { margin: 2px 0 0; font-size: 14.5px; line-height: 1.55; color: var(--ink-soft); }
.quiz-question { border: 1px solid var(--line); border-radius: 10px; padding: 18px; margin: 16px 0; }
.quiz-question legend { font-family: 'Source Serif 4', Georgia, serif; font-size: 16px; font-weight: 600; color: var(--navy); padding: 0 6px; }
.quiz-choice { display: flex; gap: 10px; align-items: flex-start; margin: 10px 0; font-size: 14.5px; color: var(--ink-soft); cursor: pointer; }
.quiz-choice input { margin-top: 3px; }
.quiz-feedback { display: none; margin-top: 16px; padding: 15px; border-radius: 8px; font-size: 14.5px; font-weight: 600; }
.quiz-feedback.correct { display: block; background: var(--practice-bg); color: #065f46; border: 1px solid #bbf7d0; }
.quiz-feedback.incorrect { display: block; background: var(--danger-bg); color: #991b1b; border: 1px solid #fecaca; }
.score-box { margin-top: 18px; padding: 18px; background: var(--info-bg); border-left: 6px solid var(--info-line); border-radius: 8px; display: none; }
.summary-list { margin: 0; padding-left: 20px; color: var(--ink-soft); }
.summary-list li { margin-bottom: 10px; line-height: 1.6; }
.reference-list { font-size: 13px; color: var(--muted); line-height: 1.6; }
.reference-list li { margin-bottom: 8px; }
.kpi-row { display: grid; grid-template-columns: repeat(3,1fr); gap: 12px; margin: 16px 0; }
.kpi { border: 1px solid var(--line); background: #fff; border-radius: 10px; padding: 14px; text-align: center; }
.kpi span { display: block; font-size: 12px; color: var(--muted); text-transform: uppercase; letter-spacing: .05em; font-weight: 700; }
.kpi strong { display: block; margin-top: 4px; color: var(--navy); font-size: 21px; }
@media (max-width: 640px) { .kpi-row { grid-template-columns: 1fr; } }