/* ============================================================
   PEQ Rule Engine — Responsive
   ============================================================ */

/* ---------- nav collapse ---------- */
@media (max-width: 1120px) {
  .main-nav {
    position: fixed;
    top: var(--header-h);
    left: 0;
    right: 0;
    flex-direction: column;
    align-items: stretch;
    gap: 2px;
    padding: 12px 20px 20px;
    background: var(--bg-elev);
    border-bottom: 1px solid var(--line);
    box-shadow: var(--shadow-lg);
    display: none;
    max-height: calc(100vh - var(--header-h));
    overflow-y: auto;
  }

  .main-nav.is-open {
    display: flex;
  }

  .main-nav a {
    padding: 12px 14px;
    font-size: var(--fs-md);
  }

  .nav-toggle {
    display: inline-flex;
  }
}

@media (max-width: 1024px) {
  .hero-grid {
    grid-template-columns: 1fr;
    gap: 40px;
  }

  .hero-flow-wrap {
    justify-content: flex-start;
  }

  .grid-4,
  .durable-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .grid-3,
  .compare-grid,
  .boundary-grid,
  .evo-source-grid,
  .doc-grid {
    grid-template-columns: 1fr;
  }

  .compare-card--featured {
    order: -1;
  }

  .split,
  .arch-layout,
  .evidence-layout {
    grid-template-columns: 1fr;
  }

  .arch-panel {
    position: static;
  }

  .demo-layout {
    grid-template-columns: 1fr;
  }

  .lifecycle {
    grid-template-columns: repeat(4, minmax(0, 1fr));
  }

  .lifecycle-stage:nth-child(5) {
    border-left: none;
  }

  .boundary-cell {
    border-left: none;
    border-top: 1px solid var(--line);
  }

  .boundary-cell:first-child {
    border-top: none;
  }
}

@media (max-width: 768px) {
  :root {
    --section-pad: 60px;
    --fs-4xl: 2.3rem;
    --fs-3xl: 1.8rem;
    --fs-2xl: 1.45rem;
  }

  .hero {
    padding: 56px 0 48px;
  }

  .footer-grid {
    grid-template-columns: 1fr;
    gap: 28px;
    padding: 40px 0 28px;
  }

  .cta-band {
    padding: 40px 28px;
  }

  .case-compare,
  .grid-2,
  .regression-stats {
    grid-template-columns: 1fr;
  }

  .core-loop {
    flex-direction: column;
    align-items: center;
  }

  .loop-arrow {
    transform: rotate(90deg);
    padding: 4px 0;
  }

  .loop-node {
    padding: 10px 16px;
  }

  .doc-section {
    padding: 22px;
  }

  .term {
    grid-template-columns: 1fr;
    gap: 6px;
  }
}

@media (max-width: 520px) {
  .container {
    padding-inline: 16px;
  }

  .grid-4,
  .durable-grid {
    grid-template-columns: 1fr;
  }

  .lifecycle {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .lifecycle-stage:nth-child(odd) {
    border-left: none;
  }

  .lifecycle-stage {
    border-top: 1px solid var(--line);
  }

  .lifecycle-stage:nth-child(-n+2) {
    border-top: none;
  }

  .hero-cta .btn {
    flex: 1;
  }

  .uc-row {
    grid-template-columns: 1fr;
    gap: 4px;
  }

  .evo-source-grid {
    grid-template-columns: 1fr;
  }

  .header-cta {
    display: none;
  }
}