:root {
  color-scheme: light;
  --bg: #edf1f3;
  --paper: #ffffff;
  --stage: #f6f8f9;
  --ink: #172128;
  --muted: #64717a;
  --line: #d5dde2;
  --line-strong: #aab8c0;
  --teal: #087d85;
  --teal-soft: #e5f3f3;
  --blue: #2d679b;
  --blue-soft: #e9f1f8;
  --green: #287750;
  --green-soft: #e7f3ec;
  --amber: #986108;
  --amber-soft: #fff3d8;
  --red: #aa3d43;
  --red-soft: #faeaec;
  --dark: #26323a;
  --code: #edf1f4;
}

* {
  box-sizing: border-box;
}

html {
  min-width: 320px;
  scroll-behavior: smooth;
}

body {
  min-width: 320px;
  margin: 0;
  overflow-x: hidden;
  background: var(--bg);
  color: var(--ink);
  font: 15px/1.68 -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  letter-spacing: 0;
}

a {
  color: var(--blue);
  text-underline-offset: 3px;
}

a:focus-visible,
summary:focus-visible {
  outline: 3px solid rgba(8, 125, 133, 0.22);
  outline-offset: 2px;
}

.masthead {
  color: #f8fafc;
  background: var(--dark);
  border-bottom: 4px solid var(--teal);
}

.masthead-inner {
  width: min(1160px, calc(100% - 40px));
  margin: 0 auto;
  padding: 32px 0 28px;
}

.breadcrumb {
  display: inline-block;
  margin-bottom: 9px;
  color: #96d7d8;
  font-size: 12px;
  font-weight: 750;
  text-decoration: none;
}

h1,
h2,
h3,
h4,
p {
  margin-top: 0;
  letter-spacing: 0;
}

h1 {
  max-width: 920px;
  margin-bottom: 9px;
  font-size: 32px;
  line-height: 1.2;
  overflow-wrap: anywhere;
}

.masthead p {
  max-width: 880px;
  margin-bottom: 0;
  color: #c8d3d9;
}

.meta {
  display: flex;
  flex-wrap: wrap;
  gap: 7px 18px;
  margin-top: 17px;
  color: #dce5e9;
  font-size: 13px;
}

.scope-strip {
  border-bottom: 1px solid var(--line);
  background: var(--amber-soft);
}

.scope-strip div {
  width: min(1160px, calc(100% - 40px));
  margin: 0 auto;
  padding: 11px 0;
  color: #624514;
  font-size: 13px;
}

.mobile-toc {
  display: none;
  border-bottom: 1px solid var(--line);
  background: var(--paper);
}

.mobile-toc summary {
  min-height: 48px;
  padding: 13px 18px;
  cursor: pointer;
  font-weight: 750;
}

.mobile-links {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  border-top: 1px solid var(--line);
}

.mobile-links a {
  min-width: 0;
  padding: 10px 18px;
  border-bottom: 1px solid var(--line);
  color: var(--ink);
  text-decoration: none;
  overflow-wrap: anywhere;
}

.page {
  width: min(1160px, calc(100% - 40px));
  margin: 0 auto;
  display: grid;
  grid-template-columns: 238px minmax(0, 1fr);
  align-items: start;
}

aside {
  position: sticky;
  top: 0;
  max-height: 100vh;
  overflow-y: auto;
  padding: 28px 22px 28px 0;
}

aside h2 {
  margin: 0 0 11px;
  color: var(--muted);
  font-size: 12px;
  text-transform: uppercase;
}

aside nav {
  border-top: 1px solid var(--line-strong);
}

aside nav a {
  display: grid;
  grid-template-columns: 29px minmax(0, 1fr);
  gap: 7px;
  padding: 9px 0;
  border-bottom: 1px solid var(--line);
  color: var(--ink);
  font-size: 13px;
  line-height: 1.35;
  text-decoration: none;
}

aside nav a:hover {
  color: var(--teal);
}

aside nav span {
  color: var(--muted);
  font-variant-numeric: tabular-nums;
}

.side-back {
  display: inline-block;
  margin-top: 16px;
  font-size: 12px;
}

main {
  min-width: 0;
  padding: 0 36px 56px;
  border-right: 1px solid var(--line);
  border-left: 1px solid var(--line);
  background: var(--paper);
}

.intro,
main section {
  padding: 28px 0;
  border-bottom: 1px solid var(--line);
  scroll-margin-top: 18px;
}

main section:last-child {
  border-bottom: 0;
}

.intro {
  color: #35434c;
}

.section-number {
  margin-bottom: 5px;
  color: var(--teal);
  font-size: 12px;
  font-weight: 800;
  font-variant-numeric: tabular-nums;
}

h2 {
  margin-bottom: 15px;
  font-size: 23px;
  line-height: 1.3;
}

h3 {
  margin: 25px 0 8px;
  font-size: 17px;
  line-height: 1.35;
}

h4 {
  margin: 0 0 6px;
  font-size: 14px;
}

p {
  margin-bottom: 11px;
  overflow-wrap: anywhere;
}

ul,
ol {
  margin: 9px 0 13px;
  padding-left: 22px;
}

li {
  margin: 5px 0;
}

code,
pre {
  border-radius: 5px;
  background: var(--code);
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;
  font-size: 13px;
}

code {
  padding: 1px 5px;
}

pre {
  max-width: 100%;
  overflow-x: auto;
  margin: 11px 0;
  padding: 13px 14px;
  line-height: 1.58;
  white-space: pre;
}

.lead,
.note,
.warning,
.boundary {
  margin: 15px 0;
  padding: 13px 15px;
  border-left: 4px solid var(--blue);
  background: var(--blue-soft);
}

.note {
  border-left-color: var(--green);
  background: var(--green-soft);
}

.warning {
  border-left-color: var(--red);
  background: var(--red-soft);
}

.boundary {
  border-left-color: var(--amber);
  background: var(--amber-soft);
}

.lead p:last-child,
.note p:last-child,
.warning p:last-child,
.boundary p:last-child {
  margin-bottom: 0;
}

.muted {
  color: var(--muted);
}

.grid-2,
.grid-3 {
  display: grid;
  gap: 12px;
  margin: 14px 0;
}

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

.grid-3 {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.fact {
  min-width: 0;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: #fbfcfd;
}

.fact h3,
.fact h4 {
  margin-top: 0;
}

.fact p:last-child,
.fact ul:last-child {
  margin-bottom: 0;
}

.table-scroll {
  max-width: 100%;
  overflow-x: auto;
  margin: 13px 0;
  border: 1px solid var(--line);
}

table {
  width: 100%;
  min-width: 620px;
  border-collapse: collapse;
  font-size: 14px;
}

th,
td {
  padding: 9px 10px;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

th:last-child,
td:last-child {
  border-right: 0;
}

tr:last-child td {
  border-bottom: 0;
}

th {
  background: #f5f8f9;
  white-space: nowrap;
}

.diagram {
  margin: 16px 0;
  padding: 17px;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: var(--stage);
}

.diagram-title {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 14px;
  padding-bottom: 9px;
  border-bottom: 1px solid var(--line);
}

.diagram-title strong {
  font-size: 14px;
}

.diagram-title span {
  color: var(--muted);
  font-size: 12px;
  text-align: right;
}

.flow-row {
  display: flex;
  align-items: stretch;
  justify-content: center;
  gap: 8px;
  min-width: 0;
}

.flow-node {
  min-width: 0;
  flex: 1 1 0;
  display: grid;
  place-content: center;
  min-height: 68px;
  padding: 10px;
  border: 1px solid #aebbc3;
  border-radius: 6px;
  background: #fff;
  text-align: center;
}

.flow-node strong {
  display: block;
  color: var(--ink);
  font-size: 14px;
}

.flow-node small {
  display: block;
  margin-top: 4px;
  color: var(--muted);
  line-height: 1.35;
}

.flow-node.blue {
  border-color: #91afc9;
  background: var(--blue-soft);
}

.flow-node.teal {
  border-color: #7fb5b8;
  background: var(--teal-soft);
}

.flow-node.green {
  border-color: #91b9a3;
  background: var(--green-soft);
}

.flow-node.amber {
  border-color: #d0ae6a;
  background: var(--amber-soft);
}

.flow-node.red {
  border-color: #d6a2a6;
  background: var(--red-soft);
}

.flow-arrow {
  flex: 0 0 22px;
  display: grid;
  place-content: center;
  color: var(--teal);
  font-size: 20px;
  font-weight: 800;
}

.flow-caption {
  margin: 11px 0 0;
  color: var(--muted);
  font-size: 12px;
  text-align: center;
}

.bit-layout {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  overflow: hidden;
  border: 1px solid var(--line-strong);
  border-radius: 6px;
  background: #fff;
}

.bit {
  min-width: 0;
  padding: 12px 8px;
  border-right: 1px solid var(--line);
  text-align: center;
}

.bit:last-child {
  border-right: 0;
}

.bit strong {
  display: block;
  overflow-wrap: anywhere;
}

.bit small {
  display: block;
  margin-top: 4px;
  color: var(--muted);
}

.bit.vpn {
  background: var(--blue-soft);
}

.bit.ppn {
  background: var(--green-soft);
}

.bit.offset {
  background: var(--amber-soft);
}

.bit.flags {
  background: var(--teal-soft);
}

.stack {
  display: grid;
  gap: 8px;
  max-width: 720px;
  margin: 0 auto;
}

.stack-level {
  position: relative;
  min-width: 0;
  padding: 11px 13px;
  border: 1px solid var(--line-strong);
  border-radius: 6px;
  background: #fff;
}

.stack-level + .stack-level::before {
  content: "↓";
  position: absolute;
  top: -19px;
  left: 50%;
  color: var(--teal);
  font-weight: 800;
  transform: translateX(-50%);
}

.stack-level strong {
  display: block;
  margin-bottom: 2px;
}

.stack-level span {
  color: var(--muted);
  font-size: 13px;
}

.tree {
  display: grid;
  gap: 10px;
  max-width: 760px;
  margin: 0 auto;
}

.tree-row {
  display: grid;
  grid-template-columns: 130px minmax(0, 1fr);
  gap: 10px;
  align-items: stretch;
}

.tree-label {
  display: grid;
  place-content: center;
  min-width: 0;
  padding: 9px;
  border: 1px solid var(--line-strong);
  border-radius: 6px;
  background: var(--teal-soft);
  color: #075f65;
  font-weight: 750;
  text-align: center;
}

.tree-content {
  min-width: 0;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: #fff;
}

.tree-content code {
  white-space: normal;
  overflow-wrap: anywhere;
}

.split-lane {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.lane {
  min-width: 0;
  padding: 13px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: #fff;
}

.lane h3 {
  margin: 0 0 9px;
  font-size: 15px;
}

.lane ol,
.lane ul {
  margin-bottom: 0;
}

.protocol {
  display: grid;
  grid-template-columns: minmax(116px, 1fr) 82px minmax(130px, 2fr);
  overflow: hidden;
  border: 1px solid var(--line-strong);
  border-radius: 6px;
  background: #fff;
}

.protocol div {
  min-width: 0;
  padding: 13px 10px;
  border-right: 1px solid var(--line);
  text-align: center;
}

.protocol div:last-child {
  border-right: 0;
}

.protocol strong {
  display: block;
  overflow-wrap: anywhere;
}

.protocol small {
  display: block;
  margin-top: 4px;
  color: var(--muted);
}

.checklist {
  margin: 13px 0;
  padding: 0;
  list-style: none;
  counter-reset: checks;
}

.checklist li {
  position: relative;
  margin: 0;
  padding: 10px 10px 10px 42px;
  border-bottom: 1px solid var(--line);
  counter-increment: checks;
}

.checklist li:first-child {
  border-top: 1px solid var(--line);
}

.checklist li::before {
  content: counter(checks, decimal-leading-zero);
  position: absolute;
  top: 10px;
  left: 7px;
  color: var(--teal);
  font: 750 12px/1.7 ui-monospace, SFMono-Regular, Menlo, monospace;
}

footer {
  width: min(1160px, calc(100% - 40px));
  margin: 0 auto;
  padding: 18px 0 28px 238px;
  color: var(--muted);
  font-size: 12px;
}

@media (max-width: 900px) {
  .mobile-toc {
    display: block;
  }

  .page {
    width: min(860px, calc(100% - 28px));
    display: block;
  }

  aside {
    display: none;
  }

  main {
    padding: 0 24px 48px;
    border-right: 1px solid var(--line);
    border-left: 1px solid var(--line);
  }

  footer {
    width: min(860px, calc(100% - 28px));
    padding-left: 0;
  }
}

@media (max-width: 680px) {
  .masthead-inner,
  .scope-strip div {
    width: min(100% - 28px, 760px);
  }

  h1 {
    font-size: 27px;
  }

  .page {
    width: 100%;
  }

  main {
    padding: 0 16px 42px;
    border: 0;
  }

  .intro,
  main section {
    padding: 24px 0;
  }

  .grid-2,
  .grid-3,
  .split-lane {
    grid-template-columns: 1fr;
  }

  .diagram {
    margin-right: -4px;
    margin-left: -4px;
    padding: 13px;
  }

  .diagram-title {
    display: block;
  }

  .diagram-title span {
    display: block;
    margin-top: 3px;
    text-align: left;
  }

  .flow-row {
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    gap: 7px;
  }

  .flow-node {
    min-height: 58px;
  }

  .flow-arrow {
    min-height: 20px;
    transform: rotate(90deg);
  }

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

  .bit {
    padding: 10px 5px;
    font-size: 12px;
  }

  .tree-row {
    grid-template-columns: 1fr;
    gap: 5px;
  }

  .tree-label {
    place-content: start;
    text-align: left;
  }

  .protocol {
    grid-template-columns: 1fr;
  }

  .protocol div {
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .protocol div:last-child {
    border-bottom: 0;
  }

  .mobile-links {
    grid-template-columns: 1fr;
  }

  footer {
    width: min(100% - 28px, 760px);
  }
}