.lesson-body .concept-triad {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 10px;
  margin: 30px 0;
}

.lesson-body .concept-triad > div {
  min-width: 0;
  padding: 18px;
  border: 1px solid var(--l-line);
  border-radius: 13px;
  background: var(--l-paper);
}

.lesson-body .concept-triad > div:nth-child(1) { border-top: 3px solid var(--l-berry); }
.lesson-body .concept-triad > div:nth-child(2) { border-top: 3px solid var(--l-forest); }
.lesson-body .concept-triad > div:nth-child(3) { border-top: 3px solid var(--l-light-brown, #A68A64); }

.lesson-body .concept-triad span {
  display: block;
  margin-bottom: 6px;
  font-family: var(--font-mono, monospace);
  font-size: 10px;
  font-weight: 600;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--l-muted);
}

.lesson-body .concept-triad strong,
.lesson-body .prefix-visual strong,
.lesson-body .subnet-grid strong,
.lesson-body .route-stack strong {
  display: block;
  color: var(--l-deep);
  line-height: 1.3;
}

.lesson-body .concept-triad p {
  margin: 8px 0 0;
  font-size: 14px;
  line-height: 1.55;
  color: var(--l-muted);
}

.lesson-body .prefix-visual {
  display: grid;
  grid-template-columns: 3fr 1fr;
  overflow: hidden;
  margin: 26px 0;
  border: 1px solid var(--l-line);
  border-radius: 13px;
}

.lesson-body .prefix-visual > div { padding: 16px 18px; background: var(--l-forest-soft); }
.lesson-body .prefix-visual > div:last-child { background: var(--l-berry-soft); }

.lesson-body .prefix-visual span,
.lesson-body .subnet-grid span,
.lesson-body .route-stack span {
  display: block;
  font-family: var(--font-mono, monospace);
  font-size: 10px;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--l-muted);
}

.lesson-body .address-strip {
  display: grid;
  grid-template-columns: repeat(8, minmax(70px, 1fr));
  gap: 5px;
  overflow-x: auto;
  margin: 24px 0;
  padding-bottom: 5px;
}

.lesson-body .address-strip span {
  padding: 11px 8px;
  border: 1px solid var(--l-line);
  border-radius: 9px;
  background: var(--l-forest-soft);
  text-align: center;
  font-family: var(--font-mono, monospace);
  font-size: 11px;
  white-space: nowrap;
}

.lesson-body .address-strip .is-reserved { background: var(--l-berry-soft); color: var(--l-berry); }

.lesson-body .subnet-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 9px;
  margin: 26px 0;
}

.lesson-body .subnet-grid > div {
  padding: 15px 17px;
  border: 1px solid var(--l-line);
  border-left: 3px solid var(--l-forest);
  border-radius: 11px;
  background: var(--l-paper);
}

.lesson-body .subnet-grid small,
.lesson-body .route-stack small { display: block; margin-top: 4px; color: var(--l-muted); }

.lesson-body .route-stack { display: grid; gap: 7px; margin: 26px 0; }

.lesson-body .route-stack > div {
  display: grid;
  grid-template-columns: 48px 1fr auto;
  align-items: center;
  gap: 12px;
  padding: 13px 15px;
  border: 1px solid var(--l-line);
  border-radius: 10px;
  background: var(--l-paper);
}

.lesson-body .route-stack > div:nth-child(2) { margin-left: 28px; }
.lesson-body .route-stack > div:nth-child(3) { margin-left: 56px; border-color: var(--l-forest); }

.lesson-body .service-path {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr) auto minmax(0, 1fr);
  align-items: center;
  gap: 10px;
  margin: 28px 0;
}

.lesson-body .service-path > div {
  min-width: 0;
  padding: 15px 16px;
  border: 1px solid var(--l-line);
  border-radius: 12px;
  background: var(--l-paper);
  text-align: center;
}

.lesson-body .service-path > b {
  color: var(--l-forest);
  font-family: var(--font-mono, monospace);
  font-size: 12px;
  white-space: nowrap;
}

.lesson-body .service-path span,
.lesson-body .diagnostic-ladder span {
  display: block;
  margin-bottom: 4px;
  font-family: var(--font-mono, monospace);
  font-size: 10px;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--l-muted);
}

.lesson-body .service-path strong,
.lesson-body .diagnostic-ladder strong {
  display: block;
  color: var(--l-deep);
  line-height: 1.3;
}

.lesson-body .service-path small,
.lesson-body .diagnostic-ladder small {
  display: block;
  margin-top: 4px;
  color: var(--l-muted);
  font-size: 12px;
}

.lesson-body .diagnostic-ladder {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 8px;
  margin: 28px 0;
}

.lesson-body .diagnostic-ladder > div {
  position: relative;
  min-width: 0;
  padding: 17px 14px 15px;
  border: 1px solid var(--l-line);
  border-top: 3px solid var(--l-forest);
  border-radius: 11px;
  background: var(--l-paper);
}

.lesson-body .diagnostic-ladder > div:nth-child(2) { border-top-color: var(--l-light-brown, #A68A64); }
.lesson-body .diagnostic-ladder > div:nth-child(3) { border-top-color: var(--l-berry); }
.lesson-body .diagnostic-ladder > div:nth-child(4) { border-top-color: var(--l-deep); }

.lesson-body .diagnostic-ladder span {
  width: 22px;
  height: 22px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 999px;
  background: var(--l-forest-soft);
  color: var(--l-deep);
}

.lesson-body .vlan-board {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 9px;
  margin: 28px 0;
}

.lesson-body .vlan-lane {
  min-width: 0;
  padding: 17px;
  border: 1px solid var(--l-line);
  border-top: 4px solid var(--l-forest);
  border-radius: 12px;
  background: var(--l-paper);
}

.lesson-body .vlan-lane:nth-child(2) { border-top-color: var(--l-light-brown, #A68A64); }
.lesson-body .vlan-lane:nth-child(3) { border-top-color: var(--l-berry); }

.lesson-body .vlan-lane span,
.lesson-body .packet-flow span {
  display: block;
  margin-bottom: 6px;
  font-family: var(--font-mono, monospace);
  font-size: 10px;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--l-muted);
}

.lesson-body .vlan-lane strong,
.lesson-body .packet-flow strong {
  display: block;
  color: var(--l-deep);
  line-height: 1.35;
}

.lesson-body .vlan-lane strong + strong { margin-top: 4px; }
.lesson-body .vlan-lane small,
.lesson-body .packet-flow small { display: block; margin-top: 5px; color: var(--l-muted); }

.lesson-body .packet-flow {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr) auto minmax(0, 1fr);
  align-items: center;
  gap: 10px;
  margin: 28px 0;
}

.lesson-body .packet-flow > div {
  min-width: 0;
  padding: 16px;
  border: 1px solid var(--l-line);
  border-radius: 12px;
  background: var(--l-paper);
  text-align: center;
}

.lesson-body .packet-flow > b {
  color: var(--l-forest);
  font-family: var(--font-mono, monospace);
}

.lesson-body .policy-matrix {
  display: grid;
  grid-template-columns: 1.2fr 1.2fr .8fr;
  overflow: hidden;
  margin: 28px 0;
  border: 1px solid var(--l-line);
  border-radius: 12px;
}

.lesson-body .policy-matrix > div {
  padding: 11px 13px;
  border-right: 1px solid var(--l-line);
  border-bottom: 1px solid var(--l-line);
  background: var(--l-paper);
  font-size: 14px;
}

.lesson-body .policy-matrix > div:nth-child(3n) { border-right: 0; }
.lesson-body .policy-matrix > div:nth-last-child(-n+3) { border-bottom: 0; }
.lesson-body .policy-matrix .is-head {
  background: var(--l-forest);
  color: #fff;
  font-weight: 600;
}
.lesson-body .policy-matrix .is-allow { color: var(--l-deep); background: var(--l-forest-soft); font-weight: 600; }
.lesson-body .policy-matrix .is-deny { color: var(--l-berry); background: var(--l-berry-soft); font-weight: 600; }

@media (max-width: 820px) {
  .lesson-body .service-path,
  .lesson-body .packet-flow {
    grid-template-columns: 1fr;
  }

  .lesson-body .service-path > b,
  .lesson-body .packet-flow > b {
    transform: rotate(90deg);
    justify-self: center;
  }

  .lesson-body .diagnostic-ladder {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .lesson-body .vlan-board { grid-template-columns: 1fr; }
}

@media (max-width: 720px) {
  .lesson-body .concept-triad,
  .lesson-body .subnet-grid { grid-template-columns: 1fr; }

  .lesson-body .route-stack > div { grid-template-columns: 42px 1fr; }
  .lesson-body .route-stack small { grid-column: 2; }
  .lesson-body .route-stack > div:nth-child(2),
  .lesson-body .route-stack > div:nth-child(3) { margin-left: 0; }
}

@media (max-width: 620px) {
  .lesson-body .policy-matrix {
    grid-template-columns: 1fr;
  }

  .lesson-body .policy-matrix > div {
    border-right: 0;
  }

  .lesson-body .policy-matrix > div:nth-last-child(-n+3) {
    border-bottom: 1px solid var(--l-line);
  }

  .lesson-body .policy-matrix > div:last-child {
    border-bottom: 0;
  }
}

@media (max-width: 520px) {
  .lesson-body .diagnostic-ladder {
    grid-template-columns: 1fr;
  }
}