/* ============================================================
   Causal Science — Marketing Measurement
   Shared stylesheet for GitHub Pages multi-page site
   ============================================================ */

/* --- Reset & Base --- */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  padding: 0;
  background: #3b4b77;
  color: #fff;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

/* --- CSS Variables (Brand) --- */
:root {
  --brand-background: #3b4b77;
  --brand-text: #ffffff;
  --brand-text-muted: rgba(255, 255, 255, 0.7);
  --brand-accent: #2dd4bf;
  --brand-border: rgba(255, 255, 255, 0.3);
  --brand-border-dim: rgba(255, 255, 255, 0.12);
  --brand-danger: #f87171;
  --brand-warning: #fbbf24;
  --brand-success: #34d399;
  --bg-card: rgba(255, 255, 255, 0.06);
  --bg-card-raised: rgba(255, 255, 255, 0.1);
  --accent-tint: rgba(45, 212, 191, 0.08);
  --danger-tint: rgba(248, 113, 113, 0.08);
  --warning-tint: rgba(251, 191, 36, 0.08);
  --font-mono: "SF Mono", "Fira Code", "Consolas", monospace;
}

/* --- Page Container --- */
.page {
  max-width: 900px;
  margin: 0 auto;
  padding: 0 24px 60px;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* --- Navigation (BACK | Title | NEXT) --- */
.sec-nav {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  padding: 12px 0;
  margin-bottom: 8px;
}
.sec-nav__header {
  justify-self: center;
  color: #fff;
  font-size: 32px;
  font-weight: 700;
  text-align: center;
  margin: 0;
}
.sec-nav__btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 10px 20px;
  border-radius: 999px;
  font-size: clamp(12px, 1.1vw, 14px);
  font-weight: 600;
  text-decoration: none;
  transition: all 0.2s ease;
  white-space: nowrap;
}
.sec-nav__btn--back {
  justify-self: start;
  background: transparent;
  border: 1px solid var(--brand-border);
  color: var(--brand-text-muted);
}
.sec-nav__btn--back:hover { border-color: #fff; color: #fff; }
.sec-nav__btn--next {
  justify-self: end;
  background: var(--brand-accent);
  border: none;
  color: var(--brand-background);
}
.sec-nav__btn--next:hover { filter: brightness(1.1); }
.sec-nav__spacer { /* placeholder when no back/next button */ }

@media (max-width: 420px) {
  .sec-nav__header { font-size: 24px; }
}

/* --- Problem Statement / Subtitle --- */
.problem-statement {
  font-size: 16px;
  color: var(--brand-text-muted);
  max-width: 700px;
  margin: 0 auto 24px;
  line-height: 1.55;
  text-align: center;
}

/* --- Content Cards --- */
.content-card {
  background: var(--bg-card);
  border: 1px solid var(--brand-border);
  border-radius: 12px;
  padding: 24px 28px;
  margin-bottom: 20px;
}

/* --- Callouts / Key Definitions --- */
.callout,
.key-definition {
  background: var(--accent-tint);
  border-left: 3px solid var(--brand-accent);
  padding: 16px 20px;
  border-radius: 0 8px 8px 0;
  margin: 16px 0;
  font-size: 14px;
  line-height: 1.6;
  color: var(--brand-text-muted);
}
.callout strong,
.key-definition strong { color: var(--brand-text); }
.callout-title {
  font-weight: 700;
  font-size: 0.8rem;
  margin-bottom: 8px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  color: var(--brand-accent);
}
.callout.warning { background: var(--warning-tint); border-left-color: var(--brand-warning); }
.callout.warning .callout-title { color: var(--brand-warning); }
.callout.danger { background: var(--danger-tint); border-left-color: var(--brand-danger); }
.callout.danger .callout-title { color: var(--brand-danger); }

/* --- Tab Buttons (pill style) --- */
.tab-selector {
  display: flex;
  justify-content: center;
  gap: 0.75rem;
  flex-wrap: wrap;
  margin-bottom: 24px;
}
.tab-btn {
  padding: 0.6rem 1.1rem;
  border: 1px solid var(--brand-border);
  border-radius: 9999px;
  background: transparent;
  color: var(--brand-text-muted);
  font-weight: 600;
  font-size: 14px;
  cursor: pointer;
  transition: all 0.2s ease-in-out;
  font-family: inherit;
}
.tab-btn:hover { border-color: var(--brand-text); color: var(--brand-text); }
.tab-btn.active { background: var(--brand-accent); color: var(--brand-background); border-color: var(--brand-accent); }

/* --- Tab Panels --- */
.tab-panel { display: none; }
.tab-panel.active { display: block; }

/* --- Buttons --- */
.btn {
  font-family: inherit;
  font-size: 14px;
  font-weight: 600;
  padding: 12px 24px;
  border: none;
  border-radius: 999px;
  cursor: pointer;
  transition: all 0.2s ease;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  white-space: nowrap;
}
.btn:disabled { opacity: 0.4; cursor: not-allowed; }
.btn-primary { background: var(--brand-accent); color: var(--brand-background); }
.btn-primary:hover:not(:disabled) { filter: brightness(1.1); transform: translateY(-1px); }
.btn-secondary { background: var(--bg-card-raised); color: var(--brand-text-muted); border: 1px solid var(--brand-border); }
.btn-secondary:hover:not(:disabled) { border-color: var(--brand-text); color: var(--brand-text); }
.btn-ghost { background: transparent; color: var(--brand-text-muted); border: 1px solid var(--brand-border); }
.btn-ghost:hover:not(:disabled) { border-color: var(--brand-text); color: var(--brand-text); }
.btn-danger { background: var(--brand-danger); color: white; padding: 6px 12px; font-size: 12px; border-radius: 6px; }
.btn-danger:hover:not(:disabled) { filter: brightness(1.1); }

.controls {
  display: flex;
  gap: 12px;
  justify-content: center;
  flex-wrap: wrap;
  margin-top: 16px;
}

/* --- Formula / Code Boxes --- */
.formula-box,
.formula {
  background: rgba(255, 255, 255, 0.04);
  border: 1px solid rgba(255, 255, 255, 0.15);
  border-radius: 8px;
  padding: 16px 20px;
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--brand-accent);
}
.formula {
  background: rgba(0, 0, 0, 0.15);
  padding: 12px 16px;
  border-radius: 6px;
  font-size: 12px;
  margin-top: 8px;
  color: var(--brand-text-muted);
  border-left: 3px solid var(--brand-border-dim);
  overflow-x: auto;
}

/* --- Interpretation Grid (2-col data) --- */
.interp-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}
.interp-item {
  background: rgba(255, 255, 255, 0.04);
  border: 1px solid var(--brand-border-dim);
  border-radius: 8px;
  padding: 14px 16px;
  text-align: center;
}

/* --- Form Inputs --- */
input[type="text"],
input[type="number"],
select {
  padding: 12px;
  border: 1px solid var(--brand-border);
  border-radius: 8px;
  font-size: 14px;
  font-family: inherit;
  background: rgba(0, 0, 0, 0.15);
  color: var(--brand-text);
  transition: border-color 0.3s;
}
input::placeholder { color: var(--brand-text-muted); opacity: 0.6; }
input:focus, select:focus { outline: none; border-color: var(--brand-accent); }

/* --- Prose Text --- */
.prose {
  color: var(--brand-text-muted);
  font-size: 15px;
  line-height: 1.6;
  margin-bottom: 16px;
}
.prose strong { color: var(--brand-text); }
.prose em { color: var(--brand-accent); font-style: normal; font-weight: 600; }

/* --- Section Cards (for multi-step UIs) --- */
.section {
  background: var(--bg-card);
  border: 1px solid var(--brand-border-dim);
  border-radius: 12px;
  padding: 24px;
  margin-bottom: 20px;
}
.section h2 {
  color: var(--brand-text);
  margin-bottom: 16px;
  font-size: 1.2rem;
  display: flex;
  align-items: center;
  gap: 12px;
}
.section p {
  color: var(--brand-text-muted);
  font-size: 14px;
  line-height: 1.6;
  margin-bottom: 12px;
}
.section p strong { color: var(--brand-text); }

.step-number {
  background: var(--brand-accent);
  color: var(--brand-background);
  width: 28px;
  height: 28px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 0.8rem;
  flex-shrink: 0;
}

/* --- Stage Cards --- */
.stage {
  background: var(--bg-card);
  border: 1px solid var(--brand-border-dim);
  border-radius: 12px;
  padding: 28px;
  margin-bottom: 20px;
}

/* --- Hidden Utility --- */
.hidden { display: none !important; }

/* --- Responsive: Tablet/Touch --- */
@media (max-width: 1366px) and (hover: none), (max-width: 1366px) and (pointer: coarse) {
  .prose,
  .callout,
  .section p,
  .problem-statement,
  .content-card p,
  .key-definition p {
    font-size: 16px !important;
  }
}

/* --- Responsive: Mobile --- */
@media (max-width: 600px) {
  .page { padding: 0 16px 40px; }
  .problem-statement { font-size: 14px; }
  .stage { padding: 20px; }
  .section { padding: 18px; }
  .content-card { padding: 18px 20px; }
  .interp-grid { grid-template-columns: 1fr; }
  .tab-btn { font-size: 13px; padding: 0.5rem 0.9rem; }
  .prose,
  .callout,
  .section p {
    font-size: 14px !important;
  }
}