* { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg: #f4f9ff;
  --surface: #ffffff;
  --surface-2: #f0f7ff;
  --text: #0f172a;
  --text-2: #64748b;
  --border: #dbeafe;
  --accent: #2563eb;
  --accent-soft: #eff6ff;
  --hover: #e0f2fe;
  --radius: 12px;
  --shadow: 0 4px 20px rgba(37,99,235,0.08);
  --topbar-h: 56px;
  --sidebar-w: 260px;
  --toc-w: 240px;
  --code-bg: #f6f8fa;
  --code-text: #24292e;
}

body.dark {
  --bg: #0b1220;
  --surface: #111827;
  --surface-2: #1e293b;
  --text: #f0f9ff;
  --text-2: #94a3b8;
  --border: #1e3a8a;
  --accent: #60a5fa;
  --accent-soft: #172554;
  --hover: #1e293b;
  --code-bg: #eef1f5;
  --code-text: #24292e;
}

html { scroll-behavior: smooth; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Microsoft YaHei", "PingFang SC", sans-serif;
  color: var(--text);
  background: var(--bg);
}

/* ===== 动感 UI ===== */
button, .node-row, .toc-item, .copy-btn, .actions button, .toolbar-actions button, .quiz-opt, .top-actions button {
  transition: color .15s ease, background-color .15s ease, border-color .15s ease, transform .15s ease, box-shadow .15s ease;
}
button:hover, .top-actions button:hover, .actions button:hover, .toolbar-actions button:hover {
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(37,99,235,0.12);
}
.node-row:hover {
  background: var(--hover);
  transform: translateX(3px);
}
.toc-item:hover {
  background: var(--hover);
  transform: translateX(4px);
}
.sidebar, .toc, .markdown-body pre, .quiz {
  box-shadow: var(--shadow);
}
input[type="search"]:focus {
  box-shadow: 0 0 0 3px rgba(37,99,235,0.12);
}

/* ===== 顶部栏 ===== */
.topbar {
  position: fixed;
  inset: 0 0 auto 0;
  height: var(--topbar-h);
  background: linear-gradient(180deg, #ffffff 0%, var(--surface-2) 100%);
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 16px 0 12px;
  z-index: 100;
  gap: 12px;
  box-shadow: 0 2px 16px rgba(37,99,235,0.06);
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 600;
  font-size: 16px;
  color: var(--text);
  flex-shrink: 0;
}
.logo-mark {
  width: 28px; height: 28px;
  background: linear-gradient(135deg, #3b82f6 0%, #2563eb 100%);
  color: #fff;
  border-radius: 8px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 14px;
  box-shadow: 0 3px 10px rgba(37,99,235,0.25);
}
.mobile-menu-toggle {
  display: none;
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text);
  font-size: 18px;
  padding: 2px 8px;
  cursor: pointer;
}
.search-box { flex: 1; max-width: 320px; }
.search-box input {
  width: 100%;
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 7px 14px;
  background: var(--surface-2);
  color: var(--text);
  font-size: 13px;
  outline: none;
}
.search-box input:focus { border-color: var(--accent); }
.top-actions { display: flex; align-items: center; gap: 8px; flex-shrink: 0; }
.top-actions button {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 6px;
  padding: 5px 12px;
  font-size: 13px;
  cursor: pointer;
}
.top-actions button:hover { background: var(--hover); }

/* ===== 主体布局 ===== */
.app {
  display: flex;
  height: calc(100vh - var(--topbar-h));
  margin-top: var(--topbar-h);
  overflow: hidden;
}

/* ===== 拖拽分隔条 ===== */
.resizer {
  width: 6px;
  flex-shrink: 0;
  cursor: col-resize;
  background: transparent;
  position: relative;
  z-index: 10;
}
.resizer::before {
  content: "";
  position: absolute;
  top: 0; bottom: 0; left: 50%;
  width: 1px;
  transform: translateX(-50%);
  background: var(--border);
  transition: background .15s, width .15s;
}
.resizer:hover::before,
.resizer.dragging::before {
  width: 2px;
  background: var(--accent);
}
body.resizing { cursor: col-resize; user-select: none; }
body.resizing iframe { pointer-events: none; }

/* ===== 左侧目录树 ===== */
.sidebar {
  width: var(--sidebar-w);
  background: var(--surface);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  flex-shrink: 0;
  overflow: hidden;
}
.sidebar-head {
  padding: 12px 14px;
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
}
.sidebar-head .logo { font-weight: 600; font-size: 15px; }
.actions { display: flex; gap: 6px; }
.actions button {
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 6px;
  padding: 3px 7px;
  font-size: 11px;
  cursor: pointer;
}
.actions button:hover { background: var(--hover); }
.tree { flex: 1; overflow-y: auto; padding: 8px; }
.sidebar-foot {
  padding: 10px 14px;
  border-top: 1px solid var(--border);
  font-size: 12px;
  color: var(--text-2);
  min-height: 38px;
}

.node { user-select: none; }
.node-row {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 5px 8px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 14px;
  color: var(--text);
}
.node-row:hover { background: var(--hover); }
.node-row.active { background: var(--accent-soft); color: var(--accent); font-weight: 500; border-left: 3px solid var(--accent); margin-left: -3px; }
.twisty { width: 14px; display: inline-block; text-align: center; font-size: 11px; color: var(--text-2); }
.icon { width: 16px; text-align: center; display: inline-flex; align-items: center; justify-content: center; }
.icon svg { display: block; }
.children { padding-left: 16px; }
.file-row .icon { color: var(--accent); }
.icon.folder { color: #c9922f; }

/* ===== 中间内容区 ===== */
.content {
  flex: 1;
  display: flex;
  flex-direction: column;
  min-width: 0;
  background: var(--bg);
  overflow: hidden;
}
.toolbar {
  padding: 10px 18px;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}
.crumb { font-size: 13px; color: var(--text-2); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.toolbar-actions { display: flex; gap: 6px; flex-shrink: 0; }
.toolbar-actions button {
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 6px;
  padding: 5px 10px;
  font-size: 12px;
  cursor: pointer;
}
.toolbar-actions button:hover { background: var(--hover); }
.toolbar-actions .danger { background: #fdecec; color: #c0392b; border-color: #f6c9c9; }
body.dark .toolbar-actions .danger { background: #3d1f1f; color: #ff9e9e; border-color: #5a2b2b; }
.toolbar-actions .danger:hover { background: #f9d9d9; }
body.dark .toolbar-actions .danger:hover { background: #4d2525; }

.markdown-body {
  flex: 1;
  overflow-y: auto;
  padding: 28px 26px;
  width: 100%;
  line-height: 1.75;
  color: var(--text);
}
.markdown-body h1, .markdown-body h2, .markdown-body h3 { scroll-margin-top: calc(var(--topbar-h) + 16px); }
.markdown-body h1 { font-size: 30px; border-bottom: 1px solid var(--border); padding-bottom: .3em; margin-bottom: .6em; }
.markdown-body h2 { font-size: 22px; margin-top: 1.6em; margin-bottom: .6em; }
.markdown-body h3 { font-size: 17px; margin-top: 1.4em; margin-bottom: .5em; }
.markdown-body p { margin: .8em 0; }
.markdown-body code {
  background: var(--surface-2);
  padding: 2px 5px;
  border-radius: 4px;
  font-family: Consolas, "SFMono-Regular", monospace;
  font-size: 13px;
}
.markdown-body pre {
  background: var(--code-bg);
  color: var(--code-text);
  padding: 16px;
  border-radius: var(--radius);
  overflow-x: auto;
  margin: .8em 0;
  position: relative;
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
}
.markdown-body pre code { background: transparent; color: inherit; padding: 0; }
/* highlight.js 适配（用我们的淡灰底，去掉主题自带 padding/背景） */
.markdown-body pre code.hljs { padding: 0; background: transparent; }
.markdown-body blockquote { border-left: 4px solid var(--accent); padding: 8px 14px; background: var(--surface-2); border-radius: 0 8px 8px 0; color: var(--text-2); margin: .8em 0; }
.markdown-body a { color: var(--accent); text-decoration: none; }
.markdown-body a:hover { text-decoration: underline; }
.markdown-body table { border-collapse: collapse; margin: .8em 0; border-radius: var(--radius); overflow: hidden; box-shadow: var(--shadow); }
.markdown-body th, .markdown-body td { border: 1px solid var(--border); padding: 8px 14px; }
.markdown-body th { background: var(--surface-2); font-weight: 600; }
.markdown-body img { max-width: 100%; }
.markdown-body ul, .markdown-body ol { padding-left: 1.6em; margin: .6em 0; }
.markdown-body .katex-display { margin: .8em 0; }

.copy-btn {
  position: absolute;
  top: 10px; right: 10px;
  background: var(--surface);
  color: var(--accent);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 4px 12px;
  font-size: 12px;
  cursor: pointer;
  transition: color .15s ease, background-color .15s ease, border-color .15s ease, transform .15s ease, box-shadow .15s ease;
}
.copy-btn:hover {
  background: var(--accent);
  color: #fff;
  transform: translateY(-1px);
  box-shadow: 0 4px 10px rgba(37,99,235,0.22);
}

.editor {
  flex: 1;
  width: 100%;
  border: none;
  resize: none;
  padding: 28px 26px;
  font-family: Consolas, "SFMono-Regular", monospace;
  font-size: 14px;
  line-height: 1.75;
  outline: none;
  background: var(--surface);
  color: var(--text);
}
.empty { color: var(--text-2); padding: 60px; text-align: center; }

/* ===== 右侧目录 ===== */
.toc {
  width: var(--toc-w);
  background: var(--surface);
  border-left: 1px solid var(--border);
  padding: 20px 16px;
  flex-shrink: 0;
  overflow-y: auto;
}
.toc-head { display: flex; align-items: center; justify-content: space-between; margin-bottom: 12px; }
.toc-title { font-size: 12px; font-weight: 600; color: var(--text-2); text-transform: uppercase; letter-spacing: .04em; }
.mobile-toc-close {
  display: none;
  background: transparent;
  border: none;
  font-size: 22px;
  line-height: 1;
  color: var(--text-2);
  cursor: pointer;
}
.toc-list { display: flex; flex-direction: column; gap: 2px; }
.toc-item {
  font-size: 13px;
  color: var(--text-2);
  text-decoration: none;
  padding: 5px 8px;
  border-radius: 6px;
  border-left: 2px solid transparent;
  transition: background .15s, color .15s, border-color .15s;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.toc-item:hover { color: var(--text); background: var(--hover); }
.toc-item.active { color: var(--accent); background: var(--accent-soft); border-left-color: var(--accent); font-weight: 500; transform: translateX(4px); }
.toc-h1 { padding-left: 8px; }
.toc-h2 { padding-left: 20px; }
.toc-h3 { padding-left: 32px; }

/* ===== 选择题 ===== */
.quiz { border: 1px solid var(--border); border-left: 4px solid var(--accent); border-radius: var(--radius); padding: 18px; margin: .9em 0; background: var(--surface); box-shadow: var(--shadow); }
.quiz-q { font-weight: 600; margin-bottom: 10px; }
.quiz-opts { display: flex; flex-direction: column; gap: 6px; }
.quiz-opt { display: flex; align-items: center; gap: 8px; padding: 6px 10px; border-radius: 8px; cursor: pointer; border: 1px solid transparent; }
.quiz-opt:hover { background: var(--hover); }
.quiz-opt.correct { background: #e7f7ec; border-color: #bfe6c9; }
body.dark .quiz-opt.correct { background: #132f1c; border-color: #2b6f42; }
.quiz-opt.wrong { background: #fdecec; border-color: #f6c9c9; }
body.dark .quiz-opt.wrong { background: #331414; border-color: #7a3535; }
.quiz-check { margin-top: 12px; background: linear-gradient(135deg, #3b82f6 0%, #2563eb 100%); color: #fff; border: none; border-radius: 8px; padding: 6px 16px; cursor: pointer; font-size: 13px; box-shadow: 0 3px 10px rgba(37,99,235,0.22); }
.quiz-check:hover { filter: brightness(1.05); transform: translateY(-1px); box-shadow: 0 5px 14px rgba(37,99,235,0.3); }
.quiz-fb { margin-top: 10px; font-size: 13px; font-weight: 600; }
.quiz-fb.ok { color: #1a9d4b; }
.quiz-fb.no { color: #d14343; }
.quiz-exp { margin-top: 12px; padding: 10px 12px; background: #f8fafc; border: 1px dashed var(--border); border-radius: 8px; font-size: 13px; line-height: 1.6; white-space: pre-wrap; }
body.dark .quiz-exp { background: #0f172a; }
.quiz-ans { font-weight: 600; margin-bottom: 6px; }
.quiz-exp-body { color: #475569; }
body.dark .quiz-exp-body { color: #94a3b8; }

/* ===== 移动端 ===== */
.overlay {
  display: none;
  position: fixed;
  inset: var(--topbar-h) 0 0 0;
  background: rgba(0,0,0,.35);
  z-index: 80;
}
.overlay.show { display: block; }
.mobile-toc-toggle {
  display: none;
  position: fixed;
  right: 20px;
  bottom: 24px;
  width: 50px;
  height: 50px;
  border-radius: 50%;
  background: var(--accent);
  color: #fff;
  border: none;
  box-shadow: 0 4px 14px rgba(0,0,0,.18);
  align-items: center;
  justify-content: center;
  font-size: 13px;
  cursor: pointer;
  z-index: 70;
}

@media (max-width: 1100px) {
  #rightResizer { display: none; }
  .toc { position: fixed; top: var(--topbar-h); right: 0; bottom: 0; width: 280px; transform: translateX(100%); transition: transform .22s ease; z-index: 90; box-shadow: -2px 0 12px rgba(0,0,0,.08); }
  .toc.open { transform: translateX(0); }
  .mobile-toc-close { display: block; }
  .mobile-toc-toggle { display: flex; }
}

/* ===== 配套练习弹窗 ===== */
.modal { position: fixed; inset: 0; z-index: 200; display: flex; align-items: center; justify-content: center; }
.modal[hidden] { display: none; }
.modal-backdrop { position: absolute; inset: 0; background: rgba(15,23,42,.5); }
.modal-dialog {
  position: relative;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: 0 20px 60px rgba(15,23,42,.18);
  width: min(760px, 92vw);
  max-height: 86vh;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  animation: modalIn .18s ease both;
  will-change: transform, opacity;
}
.modal-dialog.modal-lg { width: min(1000px, 95vw); }
@keyframes modalIn {
  from { opacity: 0; transform: translateY(10px) scale(.985); }
  to   { opacity: 1; transform: translateY(0) scale(1); }
}
.modal-header {
  padding: 14px 18px;
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: var(--surface-2);
}
.modal-header h3 { font-size: 16px; font-weight: 600; color: var(--text); }
.modal-close {
  background: transparent;
  border: none;
  font-size: 24px;
  line-height: 1;
  color: var(--text-2);
  cursor: pointer;
  padding: 0 4px;
}
.modal-close:hover { color: var(--text); }
.modal-body { padding: 18px; overflow-y: auto; flex: 1; }
.modal-actions {
  display: flex;
  justify-content: flex-end;
  gap: 10px;
  margin-top: 16px;
  padding-top: 14px;
  border-top: 1px solid var(--border);
}
.modal-actions button, .bank-toolbar button, .practice-admin-actions button, .bank-pagination button {
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 8px;
  padding: 6px 14px;
  font-size: 13px;
  cursor: pointer;
}
.modal-actions button.primary, .bank-toolbar button {
  background: linear-gradient(135deg, #3b82f6 0%, #2563eb 100%);
  color: #fff;
  border-color: transparent;
}
.modal-actions button:hover, .bank-toolbar button:hover, .practice-admin-actions button:hover, .bank-pagination button:hover {
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(37,99,235,.12);
}

.practice-toolbar, .bank-toolbar {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 14px;
  flex-wrap: wrap;
}
.practice-toolbar input, .bank-toolbar input {
  flex: 1;
  min-width: 180px;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 7px 12px;
  background: var(--bg);
  color: var(--text);
  font-size: 13px;
  outline: none;
}
.practice-toolbar input:focus, .bank-toolbar input:focus { border-color: var(--accent); }
.practice-admin-actions { display: flex; gap: 8px; }
.practice-table-wrap, .bank-table-wrap { overflow-x: auto; border-radius: 10px; border: 1px solid var(--border); }
.practice-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 13px;
  background: var(--surface);
}
.practice-table th, .practice-table td {
  padding: 10px 12px;
  text-align: left;
  border-bottom: 1px solid var(--border);
  vertical-align: middle;
}
.practice-table th {
  background: var(--surface-2);
  font-weight: 600;
  color: var(--text-2);
  white-space: nowrap;
}
.practice-table tbody tr { cursor: pointer; transition: background .15s; }
.practice-table tbody tr:hover { background: var(--hover); }
.practice-table tbody tr:last-child td { border-bottom: none; }
.col-idx { width: 60px; text-align: center; color: var(--text-2); }
.col-pid { width: 90px; text-align: center; color: var(--text-2); }
.col-check { width: 42px; text-align: center; }
.problem-link { color: var(--accent); font-weight: 500; text-decoration: none; }
.problem-link:hover { text-decoration: underline; }
.tag {
  display: inline-block;
  background: var(--accent-soft);
  color: var(--accent);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 2px 8px;
  font-size: 11px;
  margin: 2px 4px 2px 0;
  white-space: nowrap;
}
.practice-empty, .bank-empty {
  text-align: center;
  padding: 40px 20px;
  color: var(--text-2);
  font-size: 13px;
}
.bank-selected { color: var(--text-2); font-size: 13px; margin-left: auto; }
.bank-byid {
  display: flex;
  gap: 10px;
  align-items: stretch;
  margin-bottom: 14px;
  padding: 12px;
  background: var(--surface-2);
  border: 1px dashed var(--border);
  border-radius: 10px;
}
.bank-byid textarea {
  flex: 1;
  min-height: 64px;
  resize: vertical;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 8px 10px;
  background: var(--surface);
  color: var(--text);
  font-size: 13px;
  font-family: Consolas, "SFMono-Regular", monospace;
  outline: none;
}
.bank-byid textarea:focus { border-color: var(--accent); }
.bank-byid button {
  align-self: center;
  background: linear-gradient(135deg, #3b82f6 0%, #2563eb 100%);
  color: #fff;
  border: none;
  border-radius: 8px;
  padding: 8px 16px;
  font-size: 13px;
  cursor: pointer;
  white-space: nowrap;
  box-shadow: 0 3px 10px rgba(37,99,235,0.22);
}
.bank-byid button:hover { filter: brightness(1.05); transform: translateY(-1px); }
.bank-pagination {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  margin-top: 14px;
}
.bank-page-info { color: var(--text-2); font-size: 13px; }

@media (max-width: 768px) {
  #leftResizer { display: none; }
  .sidebar { position: fixed; top: var(--topbar-h); left: 0; bottom: 0; width: var(--sidebar-w); transform: translateX(-100%); transition: transform .22s ease; z-index: 90; box-shadow: 2px 0 12px rgba(0,0,0,.08); }
  .sidebar.open { transform: translateX(0); }
  .mobile-menu-toggle { display: inline-flex; }
  .search-box { max-width: none; }
  .search-box input { width: 100%; }
  .markdown-body { padding: 20px 18px; }
  .editor { padding: 20px 18px; }
  .top-actions button { padding: 5px 9px; font-size: 12px; }
  .modal-dialog { width: 96vw; max-height: 92vh; }
  .practice-toolbar, .bank-toolbar { flex-direction: column; align-items: stretch; }
  .practice-admin-actions { justify-content: flex-end; }
}