/* =========================
   Base
========================= */
:root {
  --bg: #f7f8fb;
  --surface: #ffffff;
  --surface2: #f0f3f8;
  --text: #1b1f2a;
  --muted: #5a6478;
  --border: #d9deea;

  --primary: #2f6fed;
  --primary-soft: #e8f0ff;

  --accent: #e23b6e;
  --accent-soft: #ffe9f1;

  --warning: #b35a00;
  --warning-soft: #fff3e1;

  --shadow: 0 10px 26px rgba(16, 24, 40, 0.08);
  --radius: 16px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0d111b;
    --surface: #12192a;
    --surface2: #0f1626;
    --text: #eef2ff;
    --muted: #b9c3df;
    --border: #24314b;

    --primary: #7aa7ff;
    --primary-soft: rgba(122, 167, 255, 0.15);

    --accent: #ff6f9a;
    --accent-soft: rgba(255, 111, 154, 0.15);

    --warning: #ffb25a;
    --warning-soft: rgba(255, 178, 90, 0.16);

    --shadow: 0 10px 28px rgba(0, 0, 0, 0.35);
  }
}

* {
  box-sizing: border-box;
}

html,
body {
  height: 100%;
}

body {
  margin: 0;
  font-family:
    ui-sans-serif,
    system-ui,
    -apple-system,
    'Segoe UI',
    'Noto Sans JP',
    'Hiragino Kaku Gothic ProN',
    'Meiryo',
    Arial,
    sans-serif;
  line-height: 1.85;
  color: var(--text);
  background:
    radial-gradient(1200px 600px at 10% 0%, var(--primary-soft), transparent 70%),
    radial-gradient(900px 520px at 90% 10%, var(--accent-soft), transparent 70%), var(--bg);
}

a {
  color: var(--primary);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

.container {
  width: min(980px, calc(100% - 32px));
  margin: 0 auto;
}

/* Skip link */
.skip-link {
  position: absolute;
  left: 12px;
  top: 12px;
  padding: 10px 12px;
  border-radius: 12px;
  background: var(--surface);
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
  transform: translateY(-150%);
  transition: transform 0.2s ease;
  z-index: 999;
}

.skip-link:focus {
  transform: translateY(0);
}

/* =========================
   Header
========================= */
.site-header {
  padding: 40px 0 22px;
}

.site-brand {
  margin: 0 0 8px;
  font-weight: 700;
  letter-spacing: 0.02em;
  color: var(--muted);
}

h1 {
  margin: 0;
  font-size: clamp(28px, 4vw, 40px);
  line-height: 1.25;
  letter-spacing: 0.01em;
}

.lead {
  margin: 14px 0 0;
  color: var(--muted);
  font-size: 1.05rem;
}

.header-actions {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  margin: 18px 0 0;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 14px;
  border-radius: 999px;
  background: var(--primary);
  color: white;
  border: 1px solid rgba(0, 0, 0, 0);
  font-weight: 700;
  box-shadow: var(--shadow);
}

.btn:hover {
  text-decoration: none;
  filter: brightness(0.98);
}

.btn-ghost {
  background: var(--surface);
  color: var(--primary);
  border: 1px solid var(--border);
}

/* =========================
   Layout blocks
========================= */
.toc {
  margin: 18px 0 18px;
  padding: 18px 18px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.toc h2 {
  margin: 0 0 8px;
  font-size: 1.1rem;
}

.toc ol {
  margin: 0;
  padding-left: 20px;
  color: var(--muted);
}

.toc a {
  font-weight: 650;
}

.card {
  margin: 18px 0;
  padding: 18px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.card-header h2 {
  margin: 0;
  font-size: 1.35rem;
}

.card-subtitle {
  margin: 8px 0 0;
  color: var(--muted);
}

.prose p {
  margin: 12px 0;
}

.pill {
  display: inline-block;
  padding: 1px 10px;
  border-radius: 999px;
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text);
  font-weight: 700;
  font-size: 0.95em;
}

/* two-column layout */
.grid-2 {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 14px;
  align-items: start;
  margin-top: 12px;
}

@media (max-width: 860px) {
  .grid-2 {
    grid-template-columns: 1fr;
  }
}

/* =========================
   Callouts
========================= */
.callout {
  margin-top: 14px;
  padding: 14px 14px;
  border-radius: 14px;
  border: 1px solid var(--border);
  background: var(--surface2);
}

.callout-title {
  margin: 0 0 6px;
  font-size: 1rem;
}

.callout-text {
  margin: 0;
  color: var(--muted);
}

.callout.note {
  border-color: rgba(47, 111, 237, 0.35);
  background: var(--primary-soft);
}

.callout.warning {
  border-color: rgba(179, 90, 0, 0.35);
  background: var(--warning-soft);
}

.callout.tip {
  border-color: rgba(226, 59, 110, 0.35);
  background: var(--accent-soft);
}

.list-check {
  margin: 10px 0 0;
  padding-left: 18px;
}

.list-check li {
  margin: 6px 0;
}

/* =========================
   Figures / SVG
========================= */
.figure {
  margin: 0;
  padding: 12px;
  border-radius: 14px;
  border: 1px solid var(--border);
  background: linear-gradient(180deg, var(--surface2), var(--surface));
}

.figure svg {
  width: 100%;
  height: auto;
  display: block;
  border-radius: 12px;
}

.figure figcaption {
  margin-top: 10px;
  color: var(--muted);
  font-size: 0.95rem;
}

/* SVG tokens */
.svg-panel {
  fill: var(--surface2);
}

.svg-surface {
  fill: var(--surface);
  stroke: var(--border);
  stroke-width: 2;
}

.svg-ground {
  fill: rgba(47, 111, 237, 0.1);
}

.svg-fault {
  stroke: var(--accent);
  stroke-width: 6;
  stroke-linecap: round;
  stroke-dasharray: 10 10;
}

.svg-plate {
  fill: rgba(47, 111, 237, 0.22);
  stroke: rgba(47, 111, 237, 0.55);
  stroke-width: 2;
}

.svg-plate2 {
  fill: rgba(226, 59, 110, 0.18);
  stroke: rgba(226, 59, 110, 0.55);
  stroke-width: 2;
}

.svg-plate-text {
  fill: var(--text);
  font-weight: 800;
  font-size: 18px;
}

.svg-label {
  fill: var(--muted);
  font-size: 14px;
  font-weight: 650;
}

.svg-title {
  fill: var(--text);
  font-size: 18px;
  font-weight: 900;
}

.svg-arrow {
  stroke: var(--text);
  stroke-width: 3;
  stroke-linecap: round;
  opacity: 0.75;
}

.svg-arrow-fill {
  fill: var(--text);
  opacity: 0.75;
}

.svg-arrow2 {
  stroke: var(--primary);
  stroke-width: 4;
  stroke-linecap: round;
  opacity: 0.9;
}

.svg-arrow2-fill {
  fill: var(--primary);
  opacity: 0.9;
}

.svg-focus {
  fill: var(--accent);
}

.svg-wave {
  fill: none;
  stroke: rgba(226, 59, 110, 0.55);
  stroke-width: 3;
}

.svg-axis {
  stroke: rgba(27, 31, 42, 0.35);
  stroke-width: 2;
}

@media (prefers-color-scheme: dark) {
  .svg-axis {
    stroke: rgba(238, 242, 255, 0.25);
  }
}

.svg-dot {
  fill: rgba(47, 111, 237, 0.65);
}

.svg-dot2 {
  fill: rgba(47, 111, 237, 0.28);
}

.svg-sine {
  fill: none;
  stroke: rgba(226, 59, 110, 0.85);
  stroke-width: 5;
  stroke-linecap: round;
}

.svg-mag {
  fill: rgba(47, 111, 237, 0.2);
  stroke: rgba(47, 111, 237, 0.55);
  stroke-width: 3;
}

.svg-big {
  fill: var(--text);
  font-weight: 900;
  font-size: 54px;
}

.svg-map {
  fill: rgba(226, 59, 110, 0.1);
  stroke: rgba(226, 59, 110, 0.35);
  stroke-width: 2;
}

.svg-i1 {
  fill: rgba(47, 111, 237, 0.55);
}
.svg-i2 {
  fill: rgba(226, 59, 110, 0.55);
}

.svg-japan {
  fill: rgba(47, 111, 237, 0.18);
  stroke: rgba(47, 111, 237, 0.6);
  stroke-width: 3;
}

/* =========================
   Table
========================= */
.table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 12px;
  overflow: hidden;
  border-radius: 14px;
  border: 1px solid var(--border);
}

.table caption {
  text-align: left;
  font-weight: 800;
  margin-bottom: 8px;
  color: var(--text);
}

.table th,
.table td {
  padding: 10px 12px;
  border-bottom: 1px solid var(--border);
}

.table thead th {
  background: var(--surface2);
  font-weight: 900;
}

.table tbody th {
  width: 28%;
  color: var(--muted);
  font-weight: 800;
  background: linear-gradient(180deg, var(--surface2), transparent);
}

/* =========================
   Features
========================= */
.feature-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin-top: 12px;
}

@media (max-width: 860px) {
  .feature-grid {
    grid-template-columns: 1fr;
  }
}

.feature {
  padding: 14px;
  border-radius: 14px;
  border: 1px solid var(--border);
  background: var(--surface2);
}

.feature h3 {
  margin: 0 0 6px;
  font-size: 1.05rem;
}

.feature p {
  margin: 0;
  color: var(--muted);
}

/* =========================
   Footer
========================= */
.site-footer {
  padding: 22px 0 40px;
}

.footer-text {
  margin: 0;
  color: var(--muted);
  text-align: center;
}