:root {
  --bg: #fdfdfd;
  --fg: #1a1a1a;
  --fg-secondary: #555;
  --accent: #2a6496;
  --accent-light: #e8f0f8;
  --border: #d0d0d0;
  --code-bg: #f4f4f4;
  --pre-bg: #f8f8f8;
  --table-header-bg: #eef2f7;
  --table-stripe: #f9fafb;
  --link: #2a6496;
  --link-visited: #5a4a8a;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #1a1a2e;
    --fg: #e0e0e0;
    --fg-secondary: #a0a0a0;
    --accent: #6db3f2;
    --accent-light: #1e2a3a;
    --border: #3a3a4e;
    --code-bg: #252540;
    --pre-bg: #20203a;
    --table-header-bg: #252545;
    --table-stripe: #1e1e38;
    --link: #6db3f2;
    --link-visited: #a898d8;
  }
}

*, *::before, *::after { box-sizing: border-box; }

body {
  line-height: 1.8;
  color: var(--fg);
  background: var(--bg);
  max-width: 52em;
  margin: 0 auto;
  padding: 2em 1.5em 4em;
}

body.ja {
  font-family: "Hiragino Kaku Gothic ProN", "Noto Sans JP", "Meiryo", sans-serif;
}

body.en {
  font-family: "Inter", "Segoe UI", "Helvetica Neue", Arial, sans-serif;
}

h1 {
  font-size: 1.6em;
  border-bottom: 3px solid var(--accent);
  padding-bottom: 0.4em;
  margin-top: 0;
}

h2 {
  font-size: 1.3em;
  color: var(--accent);
  border-bottom: 1px solid var(--border);
  padding-bottom: 0.3em;
  margin-top: 2.5em;
}

h3 {
  font-size: 1.1em;
  margin-top: 1.8em;
}

a { color: var(--link); text-decoration: none; }
a:hover { text-decoration: underline; }
a:visited { color: var(--link-visited); }

code {
  font-family: "JetBrains Mono", "Fira Code", "Source Code Pro", monospace;
  font-size: 0.88em;
  background: var(--code-bg);
  padding: 0.15em 0.4em;
  border-radius: 3px;
}

pre {
  background: var(--pre-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 1em 1.2em;
  overflow-x: auto;
  line-height: 1.5;
}

pre code {
  background: none;
  padding: 0;
  font-size: 0.85em;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin: 1em 0;
  font-size: 0.92em;
}

th, td {
  border: 1px solid var(--border);
  padding: 0.5em 0.8em;
  text-align: left;
}

th {
  background: var(--table-header-bg);
  font-weight: 600;
}

tr:nth-child(even) td { background: var(--table-stripe); }

strong { font-weight: 700; }

ul, ol { padding-left: 1.5em; }
li { margin-bottom: 0.3em; }

hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: 2.5em 0;
}

.lang-link {
  text-align: right;
  font-size: 0.9em;
  margin-bottom: 1em;
}

nav.doc-nav {
  margin-top: 3em;
  padding-top: 1.5em;
  border-top: 2px solid var(--border);
}

nav.doc-nav h2 {
  font-size: 1em;
  border-bottom: none;
  margin-top: 0;
  padding-bottom: 0;
}

nav.doc-nav ul {
  list-style: none;
  padding-left: 0;
}

nav.doc-nav li {
  margin-bottom: 0.5em;
}

.diagram {
  background: var(--pre-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 1em 1.2em;
  overflow-x: auto;
  font-family: "JetBrains Mono", "Fira Code", monospace;
  font-size: 0.82em;
  line-height: 1.4;
  white-space: pre;
}

.note {
  background: var(--accent-light);
  border-left: 4px solid var(--accent);
  padding: 0.8em 1.2em;
  margin: 1.2em 0;
  border-radius: 0 6px 6px 0;
}

/* --- CSS-based diagrams --- */

.arch-grid {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 0.8em;
  margin: 1.5em 0;
}

.arch-grid .box {
  border: 2px solid var(--accent);
  border-radius: 6px;
  padding: 0.6em 0.8em;
  background: var(--accent-light);
  text-align: center;
  font-size: 0.88em;
}

.arch-grid .box .name { font-weight: 700; }
.arch-grid .box .desc { font-size: 0.85em; color: var(--fg-secondary); margin-top: 0.2em; }

.arch-grid .arrow {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.4em;
  color: var(--accent);
  padding: 0;
  border: none;
  background: none;
}

.arch-grid .label {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.82em;
  color: var(--fg-secondary);
  border: none;
  background: none;
  padding: 0;
}

.layer-header {
  text-align: center;
  font-size: 0.82em;
  font-weight: 600;
  color: var(--fg-secondary);
  padding-bottom: 0.3em;
}

.tree-diagram {
  background: var(--pre-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 1em 1.2em;
  margin: 1em 0;
  font-size: 0.9em;
  line-height: 1.6;
}

.tree-diagram ul {
  list-style: none;
  padding-left: 1.5em;
  margin: 0;
  border-left: 2px solid var(--border);
}

.tree-diagram > ul {
  border-left: none;
  padding-left: 0;
}

.tree-diagram li {
  position: relative;
  margin-bottom: 0.2em;
}

.tree-diagram li::before {
  content: "";
  position: absolute;
  left: -1.5em;
  top: 0.7em;
  width: 1.2em;
  border-bottom: 2px solid var(--border);
}

.tree-diagram > ul > li::before { display: none; }

.tree-diagram .label { font-weight: 600; }
.tree-diagram .desc { color: var(--fg-secondary); font-size: 0.9em; }

.partition-diagram {
  border: 2px solid var(--accent);
  border-radius: 6px;
  margin: 1em 0;
  overflow: hidden;
  font-size: 0.9em;
}

.partition-diagram .part {
  padding: 0.6em 1em;
  border-bottom: 1px solid var(--border);
}

.partition-diagram .part:last-child { border-bottom: none; }

.partition-diagram .part-title {
  font-weight: 600;
  margin-bottom: 0.3em;
}

.partition-diagram .part-files {
  padding-left: 1.5em;
  color: var(--fg-secondary);
  font-size: 0.92em;
}

.partition-diagram .part-files .highlight {
  color: var(--accent);
  font-weight: 600;
}

.flow-diagram {
  background: var(--pre-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 1em 1.2em;
  margin: 1em 0;
}

.flow-diagram ol {
  list-style: none;
  padding-left: 0;
  margin: 0;
  counter-reset: flow;
}

.flow-diagram > ol > li {
  counter-increment: flow;
  margin-bottom: 0.8em;
  padding-left: 2em;
  position: relative;
}

.flow-diagram > ol > li::before {
  content: counter(flow) ".";
  position: absolute;
  left: 0;
  font-weight: 700;
  color: var(--accent);
}

.flow-diagram > ol > li::after {
  content: "↓";
  display: block;
  text-align: center;
  color: var(--accent);
  font-size: 1.2em;
  margin-top: 0.3em;
}

.flow-diagram > ol > li:last-child::after { display: none; }

.flow-diagram ul {
  list-style: none;
  padding-left: 1em;
  margin: 0.2em 0 0;
}

.flow-diagram ul li::before {
  content: "├ ";
  color: var(--accent);
  font-family: monospace;
}

.flow-diagram ul li:last-child::before {
  content: "└ ";
}

.flow-diagram .step-title { font-weight: 600; }

.update-diagram {
  background: var(--pre-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 1em 1.2em;
  margin: 1em 0;
  font-size: 0.9em;
}

.update-diagram .step {
  display: flex;
  align-items: center;
  gap: 0.8em;
  margin-bottom: 0.4em;
  font-family: "JetBrains Mono", "Fira Code", monospace;
  font-size: 0.92em;
}

.update-diagram .from { font-weight: 600; min-width: 7em; text-align: right; }
.update-diagram .arrow { color: var(--accent); }
.update-diagram .to { font-weight: 600; min-width: 7em; }
.update-diagram .desc { color: var(--fg-secondary); font-size: 0.9em; }

.boot-flow {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.4em;
  background: var(--pre-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 0.8em 1em;
  margin: 1em 0;
  font-size: 0.88em;
}

.boot-flow .stage {
  background: var(--accent-light);
  border: 1px solid var(--accent);
  border-radius: 4px;
  padding: 0.3em 0.6em;
  font-weight: 600;
}

.boot-flow .arrow {
  color: var(--accent);
  font-size: 1.2em;
}

/* --- Footnotes --- */

.footnotes {
  margin-top: 2.5em;
  padding-top: 1em;
  border-top: 1px solid var(--border);
  font-size: 0.88em;
  color: var(--fg-secondary);
}

.footnotes ol {
  padding-left: 1.5em;
}

.footnotes li {
  margin-bottom: 0.5em;
}

/* --- Last updated / Update history --- */

.last-updated {
  text-align: right;
  font-size: 0.85em;
  color: var(--fg-secondary);
  margin-top: 0;
  margin-bottom: -0.5em;
}

.update-history {
  margin-top: 3em;
  padding-top: 1.5em;
  border-top: 1px solid var(--border);
  font-size: 0.92em;
}

.update-history h2 {
  font-size: 1em;
  border-bottom: none;
  margin-top: 0;
  padding-bottom: 0;
}

.update-history ul {
  list-style: none;
  padding-left: 0;
}

.update-history li {
  margin-bottom: 0.4em;
}

.update-history time {
  font-weight: 600;
  color: var(--fg-secondary);
}

.history-link {
  font-size: 0.95em;
  margin-top: 0.8em;
}

.history-docs {
  font-size: 0.9em;
  color: var(--fg-secondary);
}