:root {
  --color-bg: #f4f8fd;
  --color-bg-panel: #ffffff;
  --color-text: #263043;
  --color-text-muted: #64748b;
  --color-border: #dbe6f3;
  --color-accent: #1a5fc4;
  --color-accent-strong: #124a9e;
  --color-accent-bg: #eaf3fd;
  --color-link: #14539e;
  --color-shadow: rgba(20, 62, 120, 0.08);
  --color-good-bg: #e7f8ee;
  --color-good-border: #b8e6c9;
  --color-good-text: #1f7a43;
  --color-caution-bg: #fff3e0;
  --color-caution-border: #ffd9a0;
  --color-caution-text: #9a6400;
  --nav-width: 300px;
  --header-height: 60px;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  background: var(--color-bg);
  color: var(--color-text);
  font-family: "Hiragino Sans", "Hiragino Kaku Gothic ProN", "Yu Gothic", "Noto Sans JP", "Segoe UI", sans-serif;
}

/* ---------- Header ---------- */

.app-header {
  height: var(--header-height);
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 0 20px;
  background: var(--color-bg-panel);
  border-bottom: 1px solid var(--color-border);
  box-shadow: 0 1px 4px var(--color-shadow);
  position: sticky;
  top: 0;
  z-index: 30;
}

.nav-toggle {
  display: none;
  font-size: 20px;
  background: none;
  border: 1px solid var(--color-border);
  border-radius: 6px;
  width: 38px;
  height: 38px;
  cursor: pointer;
  flex-shrink: 0;
}

.app-title {
  font-size: 16px;
  font-weight: 600;
  margin: 0;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  color: var(--color-accent);
}

.search-box {
  position: relative;
  margin-left: auto;
  width: 320px;
  max-width: 45vw;
}

#searchInput {
  width: 100%;
  padding: 8px 12px;
  font-size: 14px;
  border: 1px solid var(--color-border);
  border-radius: 8px;
  background: var(--color-bg);
  color: var(--color-text);
}

#searchInput:focus {
  outline: 2px solid var(--color-accent);
  outline-offset: 1px;
}

.search-results {
  position: absolute;
  top: calc(100% + 6px);
  left: 0;
  right: 0;
  max-height: 60vh;
  overflow-y: auto;
  background: var(--color-bg-panel);
  border: 1px solid var(--color-border);
  border-radius: 8px;
  box-shadow: 0 8px 24px rgba(0,0,0,0.12);
  z-index: 40;
}

.search-result-item {
  display: block;
  width: 100%;
  text-align: left;
  padding: 10px 14px;
  border: none;
  border-bottom: 1px solid var(--color-border);
  background: none;
  cursor: pointer;
  font-size: 13px;
  color: var(--color-text);
}

.search-result-item:last-child { border-bottom: none; }
.search-result-item:hover { background: var(--color-accent-bg); }

.search-result-id {
  font-weight: 600;
  color: var(--color-accent);
  margin-right: 6px;
}

.search-result-snippet {
  display: block;
  color: var(--color-text-muted);
  font-size: 12px;
  margin-top: 3px;
}

.search-empty, .search-status {
  padding: 12px 14px;
  font-size: 13px;
  color: var(--color-text-muted);
}

.search-warning {
  padding: 8px 14px;
  font-size: 12px;
  color: var(--color-caution-text);
  background: var(--color-caution-bg);
  border-bottom: 1px solid var(--color-border);
}

.search-warning button {
  margin-left: 8px;
  font-size: 12px;
  border: 1px solid var(--color-caution-border);
  background: #fff;
  color: var(--color-caution-text);
  border-radius: 4px;
  padding: 2px 8px;
  cursor: pointer;
}

/* ---------- Body layout ---------- */

.app-body {
  display: flex;
  align-items: stretch;
  min-height: calc(100vh - var(--header-height));
}

.side-nav {
  width: var(--nav-width);
  flex-shrink: 0;
  border-right: 1px solid var(--color-border);
  background: var(--color-bg-panel);
  box-shadow: 1px 0 4px var(--color-shadow);
  overflow-y: auto;
  position: sticky;
  top: var(--header-height);
  height: calc(100vh - var(--header-height));
}

.nav-content { padding: 16px 8px 40px; }

.nav-loading, .nav-error {
  padding: 16px;
  font-size: 14px;
}

.nav-error {
  color: #b23b3b;
  background: #fdecec;
  border: 1px solid #f3c6c6;
  border-radius: 8px;
  margin: 8px;
  line-height: 1.7;
}

.nav-warning {
  color: var(--color-caution-text);
  background: var(--color-caution-bg);
  border: 1px solid var(--color-caution-border);
  border-radius: 8px;
  margin: 8px;
  padding: 12px 14px;
  font-size: 12.5px;
  line-height: 1.7;
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.nav-section-title {
  font-size: 13px;
  font-weight: 700;
  color: var(--color-accent);
  padding: 14px 12px 6px;
  margin: 0;
  letter-spacing: 0.02em;
}

.nav-lesson-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-lesson-item { margin: 0; }

.nav-lesson-link {
  display: block;
  width: 100%;
  text-align: left;
  padding: 8px 12px 8px 16px;
  border: none;
  background: none;
  cursor: pointer;
  font-size: 13.5px;
  line-height: 1.5;
  color: var(--color-text);
  border-radius: 6px;
}

.nav-lesson-link:hover { background: var(--color-accent-bg); }

.nav-lesson-link.active {
  background: var(--color-accent);
  color: #fff;
  font-weight: 600;
  box-shadow: 0 1px 4px var(--color-shadow);
}

.nav-lesson-id {
  display: block;
  font-size: 11px;
  font-weight: 700;
  opacity: 0.75;
  margin-bottom: 2px;
}

.nav-scrim {
  display: none;
}

/* ---------- Main pane ---------- */

.main-pane {
  flex: 1;
  min-width: 0;
  display: flex;
  flex-direction: column;
}

.position-bar {
  padding: 10px 24px;
  border-bottom: 1px solid var(--color-border);
  background: var(--color-bg-panel);
  font-size: 13px;
  color: var(--color-text-muted);
  position: sticky;
  top: var(--header-height);
  z-index: 20;
}

.position-label strong { color: var(--color-accent); }

.lesson-content {
  flex: 1;
  width: 100%;
  max-width: 780px;
  margin: 0 auto;
  padding: 40px 32px 60px;
  font-size: 17px;
  line-height: 1.95;
  letter-spacing: 0.01em;
}

.content-loading, .content-error {
  color: var(--color-text-muted);
}

.content-error {
  color: #b23b3b;
  background: #fdecec;
  border: 1px solid #f3c6c6;
  border-radius: 8px;
  padding: 16px;
}

.lesson-content h1,
.lesson-content h2,
.lesson-content h3,
.lesson-content h4 {
  color: var(--color-accent);
  line-height: 1.5;
  font-weight: 700;
}

.lesson-content h1 {
  font-size: 1.6em;
  margin: 0 0 28px;
  padding-bottom: 14px;
  border-bottom: 2px solid var(--color-border);
}

.lesson-content h2 {
  font-size: 1.3em;
  margin: 48px 0 20px;
}

.lesson-content h3 {
  font-size: 1.12em;
  margin: 36px 0 16px;
}

.lesson-content h4 {
  font-size: 1.02em;
  margin: 28px 0 12px;
}

.lesson-content p {
  margin: 0 0 22px;
}

.lesson-content ul,
.lesson-content ol {
  margin: 0 0 22px;
  padding-left: 1.6em;
}

.lesson-content li {
  margin: 0 0 10px;
}

.lesson-content strong {
  color: var(--color-accent);
  font-weight: 700;
}

.lesson-content blockquote {
  margin: 0 0 24px;
  padding: 14px 20px;
  border-left: 4px solid var(--color-accent);
  background: var(--color-accent-bg);
  color: var(--color-text);
  border-radius: 0 6px 6px 0;
}

.lesson-content blockquote p:last-child { margin-bottom: 0; }

.lesson-content code {
  font-family: "SFMono-Regular", Consolas, Menlo, monospace;
  font-size: 0.9em;
  background: var(--color-accent-bg);
  padding: 2px 6px;
  border-radius: 4px;
}

.lesson-content pre {
  background: var(--color-accent-bg);
  color: var(--color-text);
  border: 1px solid var(--color-border);
  padding: 18px 20px;
  border-radius: 8px;
  overflow-x: auto;
  margin: 0 0 24px;
  line-height: 1.6;
}

.lesson-content pre code {
  background: none;
  padding: 0;
  color: inherit;
}

.lesson-content hr {
  border: none;
  border-top: 1px solid var(--color-border);
  margin: 40px 0;
}

.lesson-content a {
  color: var(--color-link);
  text-decoration: underline;
}

.table-scroll {
  overflow-x: auto;
  margin: 0 0 28px;
  border: 1px solid var(--color-border);
  border-radius: 8px;
}

.lesson-content table {
  border-collapse: collapse;
  width: 100%;
  font-size: 0.92em;
}

.lesson-content th,
.lesson-content td {
  border: 1px solid var(--color-border);
  padding: 10px 14px;
  text-align: left;
  vertical-align: top;
  line-height: 1.6;
}

.lesson-content th {
  background: var(--color-accent-bg);
  color: var(--color-accent);
  font-weight: 700;
  white-space: nowrap;
}

.lesson-content tr:nth-child(even) td {
  background: #f8fafd;
}

.prev-next-bar {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  padding: 16px 32px 32px;
  max-width: 780px;
  margin: 0 auto;
  width: 100%;
}

.nav-btn {
  flex: 1;
  padding: 14px 18px;
  font-size: 14px;
  font-weight: 600;
  border: 1px solid var(--color-border);
  background: var(--color-bg-panel);
  border-radius: 8px;
  cursor: pointer;
  color: var(--color-accent);
}

.nav-btn:hover:not(:disabled) {
  background: var(--color-accent-bg);
  border-color: var(--color-accent);
}

.nav-btn:disabled {
  opacity: 0.4;
  cursor: default;
}

.next-btn { text-align: right; }

/* ---------- Responsive ---------- */

@media (max-width: 900px) {
  .search-box { width: 220px; }
}

@media (max-width: 768px) {
  .nav-toggle { display: inline-flex; align-items: center; justify-content: center; }

  .app-title { font-size: 14px; }

  .search-box { width: 160px; max-width: 40vw; }

  .side-nav {
    position: fixed;
    top: var(--header-height);
    left: 0;
    height: calc(100vh - var(--header-height));
    z-index: 50;
    transform: translateX(-100%);
    transition: transform 0.2s ease;
    box-shadow: 4px 0 16px rgba(20, 62, 120, 0.18);
  }

  .side-nav.open { transform: translateX(0); }

  .nav-scrim {
    display: none;
    position: fixed;
    inset: var(--header-height) 0 0 0;
    background: rgba(15, 42, 82, 0.35);
    z-index: 45;
  }

  .nav-scrim.visible { display: block; }

  .lesson-content {
    padding: 28px 18px 48px;
    font-size: 16px;
  }

  .prev-next-bar { padding: 12px 18px 28px; }

  .position-bar { padding: 8px 16px; }
}