:root {
    --bg: #ffffff; --bg-sidebar: #f7f8fa; --text: #2d3436; --text-secondary: #636e72;
    --primary: #0984e3; --primary-light: #d6eaf8; --accent: #00b894; --border: #dfe6e9;
    --code-bg: #f1f2f6; --table-stripe: #f8f9fa; --table-header: #0984e3;
    --answer-bg: #e8f5e9; --answer-border: #4caf50; --shadow: 0 2px 8px rgba(0,0,0,0.08);
}
[data-theme="dark"] {
    --bg: #1a1a2e; --bg-sidebar: #16213e; --text: #e0e0e0; --text-secondary: #a0a0a0;
    --primary: #74b9ff; --primary-light: #2d3436; --accent: #55efc4; --border: #2d3436;
    --code-bg: #2d3436; --table-stripe: #222831; --table-header: #0984e3;
    --answer-bg: #1b3a1b; --answer-border: #4caf50; --shadow: 0 2px 8px rgba(0,0,0,0.3);
}

* { margin:0; padding:0; box-sizing:border-box; }
body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
    background: var(--bg); color: var(--text); line-height: 1.8;
    display: flex; min-height: 100vh;
}
.sidebar {
    position: fixed; top: 0; left: 0; width: 240px; height: 100vh;
    background: var(--bg-sidebar); border-right: 1px solid var(--border);
    overflow-y: auto; padding: 18px; z-index: 100; transition: transform 0.3s;
}
.sidebar h3 { font-size: 1.0em; color: var(--primary); margin-bottom: 12px; padding-bottom: 8px; border-bottom: 2px solid var(--primary); }
.toc-list { list-style: none; font-size: 0.85em; }
.toc-list a { color: var(--text-secondary); text-decoration: none; display: block; padding: 2px 0; transition: color 0.2s; }
.toc-list a:hover { color: var(--primary); }
.toc-sub { list-style: none; padding-left: 12px; font-size: 0.94em; }

/* ── Top nav ── */
.top-nav {
    position: fixed; top: 0; left: 240px; right: 0; z-index: 99;
    background: var(--bg); border-bottom: 1px solid var(--border);
    padding: 6px 16px; display: flex; align-items: center; gap: 2px; flex-wrap: wrap;
}
.top-nav a {
    color: var(--primary); text-decoration: none; padding: 5px 10px;
    border-radius: 14px; transition: background 0.2s; font-size: 0.85em; white-space: nowrap;
}
.top-nav a:hover { background: var(--primary-light); }
.top-nav a.active { background: var(--primary); color: #fff; font-weight: 600; }
.top-nav .sep { color: var(--border); font-size: 0.8em; margin: 0 2px; user-select: none; }
.sub-nav {
    position: fixed; top: 40px; left: 240px; right: 0; z-index: 98;
    background: var(--bg); border-bottom: 1px solid var(--border);
    padding: 4px 16px; display: flex; align-items: center; gap: 2px; flex-wrap: wrap;
}
.sub-nav a {
    color: var(--text-secondary); text-decoration: none; padding: 3px 9px;
    border-radius: 12px; font-size: 0.8em; transition: background 0.2s; white-space: nowrap;
}
.sub-nav a:hover { background: var(--primary-light); color: var(--primary); }
.sub-nav a.active { background: var(--accent); color: #fff; font-weight: 600; }
.sub-nav .label { color: var(--text-secondary); font-size: 0.78em; margin-right: 6px; font-weight: 600; }

.theme-toggle {
    position: fixed; top: 6px; right: 16px; z-index: 200;
    background: var(--bg); border: 1px solid var(--border); border-radius: 16px;
    padding: 3px 12px; cursor: pointer; font-size: 0.8em; color: var(--text);
    box-shadow: var(--shadow);
}
.theme-toggle:hover { background: var(--primary-light); }
.mobile-nav { display: none; position: fixed; bottom: 20px; left: 20px; z-index: 200;
    width: 44px; height: 44px; border-radius: 50%; background: var(--primary);
    color: #fff; border: none; font-size: 1.2em; cursor: pointer;
    box-shadow: 0 4px 12px rgba(0,0,0,0.3);
}

/* ── Main ── */
.main { margin-left: 240px; padding: 82px 36px 36px; max-width: 880px; width: 100%; min-height: 100vh; }
@media (max-width: 900px) {
    .sidebar { transform: translateX(-100%); }
    .sidebar.open { transform: translateX(0); }
    .main { margin-left: 0; padding: 82px 14px 30px; }
    .top-nav { left: 0; padding: 5px 8px; }
    .sub-nav { left: 0; top: 36px; padding: 3px 8px; }
    .theme-toggle { top: 44px; right: 8px; }
    .mobile-nav { display: flex; align-items: center; justify-content: center; }
}

/* ── Page nav (prev/next) ── */
.page-nav { display: flex; justify-content: space-between; margin-top: 36px; padding-top: 18px; border-top: 1px solid var(--border); }
.page-nav a {
    color: var(--primary); text-decoration: none; padding: 8px 20px;
    border: 1px solid var(--border); border-radius: 20px; font-size: 0.88em;
    transition: all 0.2s;
}
.page-nav a:hover { background: var(--primary-light); border-color: var(--primary); }

/* ── Typography ── */
h1 { font-size: 1.6em; color: var(--primary); margin: 16px 0 10px; border-bottom: 3px solid var(--primary); padding-bottom: 6px; }
h2 { font-size: 1.3em; color: var(--text); margin: 26px 0 10px; border-left: 4px solid var(--accent); padding-left: 10px; }
h3 { font-size: 1.1em; color: var(--primary); margin: 20px 0 8px; }
h4 { font-size: 0.98em; color: var(--text); margin: 14px 0 6px; }
p { margin: 5px 0; }
strong { color: var(--primary); }
blockquote { border-left: 4px solid var(--accent); padding: 10px 14px; margin: 10px 0; background: var(--primary-light); border-radius: 0 8px 8px 0; color: var(--text-secondary); }
hr { border: none; border-top: 1px solid var(--border); margin: 24px 0; }

.table-wrap { overflow-x: auto; margin: 10px 0 14px; border-radius: 8px; box-shadow: var(--shadow); }
table { width: 100%; border-collapse: collapse; font-size: 0.83em; }
thead { background: var(--table-header); }
thead th { color: #fff; padding: 6px 10px; text-align: left; font-weight: 600; white-space: nowrap; }
tbody td { padding: 5px 10px; border-bottom: 1px solid var(--border); }
tbody tr:nth-child(even) { background: var(--table-stripe); }
tbody tr:hover { background: var(--primary-light); }

.answer-box { margin: 12px 0; border: 2px solid var(--answer-border); border-radius: 10px; overflow: hidden; background: var(--answer-bg); }
.answer-box summary { padding: 8px 14px; cursor: pointer; font-weight: 700; color: var(--answer-border); user-select: none; list-style: none; }
.answer-box summary::-webkit-details-marker { display: none; }
.answer-box summary::before { content: "🔒 "; }
.answer-box[open] summary::before { content: "🔓 "; }
.answer-box[open] summary { border-bottom: 1px solid var(--answer-border); }
.answer-box p, .answer-box ol, .answer-box ul { padding: 4px 14px; }

code { background: var(--code-bg); padding: 2px 5px; border-radius: 3px; font-size: 0.89em; font-family: "Fira Code", "Consolas", monospace; }
pre { background: var(--code-bg); padding: 12px; border-radius: 8px; overflow-x: auto; margin: 8px 0; }
pre code { background: none; padding: 0; }

@media print {
    .sidebar, .top-nav, .sub-nav, .theme-toggle, .mobile-nav, .page-nav { display: none; }
    .main { margin-left: 0; padding: 0; }
    body { font-size: 11pt; }
    .answer-box { break-inside: avoid; }
}

/* ── 学习进度追踪 ── */
a.completed::after {
    content: ' \2713';
    color: var(--accent);
    font-weight: 700;
    margin-left: 4px;
}
.sub-nav a.active.completed::after,
.top-nav a.active.completed::after {
    color: #fff;
}

.top-nav a .phase-badge {
    font-size: 0.75em;
    margin-left: 4px;
    padding: 1px 5px;
    border-radius: 8px;
    background: var(--border);
    color: var(--text-secondary);
}
.top-nav a.active .phase-badge {
    background: rgba(255,255,255,0.25);
    color: #fff;
}
.top-nav a.phase-partial .phase-badge {
    background: var(--primary-light);
    color: var(--primary);
}
.top-nav a.phase-done .phase-badge {
    background: var(--accent);
    color: #fff;
}
.top-nav a.active.phase-partial .phase-badge,
.top-nav a.active.phase-done .phase-badge {
    background: rgba(255,255,255,0.9);
    color: var(--primary);
}

.overall-progress { margin: 16px 0 24px; }
.progress-total { margin-bottom: 14px; }
.progress-label {
    display: flex;
    justify-content: space-between;
    font-size: 0.85em;
    margin-bottom: 4px;
    color: var(--text-secondary);
}
.progress-bar {
    height: 10px;
    background: var(--border);
    border-radius: 5px;
    overflow: hidden;
}
.progress-fill {
    display: block;
    height: 100%;
    background: var(--accent);
    width: 0;
    transition: width 0.3s ease;
}
.progress-summary { display: grid; gap: 8px; }

.progress-toggle-btn {
    position: fixed;
    bottom: 20px;
    right: 20px;
    z-index: 200;
    background: var(--text-secondary);
    color: #fff;
    border: none;
    border-radius: 20px;
    padding: 8px 16px;
    font-size: 0.85em;
    cursor: pointer;
    box-shadow: var(--shadow);
}
.progress-toggle-btn.completed { background: var(--accent); }
.progress-toggle-btn:hover { opacity: 0.9; }

@media (max-width: 900px) {
    .progress-toggle-btn {
        bottom: 16px;
        right: 16px;
        padding: 6px 12px;
    }
}

/* ── 全站搜索 ── */
.search-box {
    position: relative;
    display: flex;
    align-items: center;
    margin-left: 6px;
}
.search-input {
    width: 180px;
    padding: 5px 12px;
    border: 1px solid var(--border);
    border-radius: 16px;
    background: var(--bg);
    color: var(--text);
    font-size: 0.85em;
    outline: none;
    transition: border-color 0.2s, box-shadow 0.2s;
}
.search-input:focus {
    border-color: var(--primary);
    box-shadow: 0 0 0 2px var(--primary-light);
}
.search-input::placeholder { color: var(--text-secondary); }

.search-dropdown {
    display: none;
    position: absolute;
    top: calc(100% + 6px);
    right: 0;
    min-width: 280px;
    max-width: 420px;
    max-height: 70vh;
    overflow-y: auto;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: 10px;
    box-shadow: var(--shadow);
    z-index: 300;
    padding: 6px 0;
}
.search-dropdown.open { display: block; }

.search-result-group { margin-bottom: 4px; }
.search-result-header {
    padding: 6px 14px;
    font-size: 0.75em;
    font-weight: 700;
    color: var(--text-secondary);
    border-bottom: 1px solid var(--border);
}
.search-result-item {
    display: block;
    padding: 7px 14px;
    color: var(--text);
    text-decoration: none;
    transition: background 0.15s;
}
.search-result-item:hover,
.search-result-item.active {
    background: var(--primary-light);
}
.search-result-title { font-size: 0.9em; line-height: 1.4; }
.search-result-section {
    font-size: 0.78em;
    color: var(--text-secondary);
    margin-top: 2px;
}
.search-status {
    padding: 14px;
    font-size: 0.85em;
    color: var(--text-secondary);
    text-align: center;
}
.search-dropdown mark {
    background: #ffeaa7;
    color: inherit;
    border-radius: 2px;
    padding: 0 1px;
}
[data-theme="dark"] .search-dropdown mark { background: #b7791f; }

@media (max-width: 900px) {
    .search-input { width: 130px; }
    .search-dropdown {
        right: 0;
        min-width: calc(100vw - 32px);
        max-width: calc(100vw - 32px);
    }
}

/* ── 搜索热键提示 ── */
.search-shortcut {
    position: absolute;
    right: 10px;
    top: 50%;
    transform: translateY(-50%);
    font-size: 0.7em;
    padding: 1px 5px;
    border-radius: 4px;
    background: var(--border);
    color: var(--text-secondary);
    pointer-events: none;
}
.search-box:focus-within .search-shortcut { display: none; }

/* ── 搜索历史 ── */
.search-history-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 6px 14px;
    font-size: 0.75em;
    color: var(--text-secondary);
    border-bottom: 1px solid var(--border);
}
.search-history-clear {
    background: none;
    border: none;
    color: var(--primary);
    cursor: pointer;
    font-size: 0.9em;
    padding: 0;
}
.search-history-clear:hover { text-decoration: underline; }
.search-history-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 7px 14px;
    color: var(--text);
    text-decoration: none;
    transition: background 0.15s;
}
.search-history-item:hover,
.search-history-item.active { background: var(--primary-light); }
.search-history-arrow { color: var(--text-secondary); font-size: 0.85em; }

.search-result-footer {
    padding: 8px 14px;
    text-align: center;
    font-size: 0.85em;
    border-top: 1px solid var(--border);
}
.search-result-footer a { color: var(--primary); text-decoration: none; }
.search-result-footer a:hover { text-decoration: underline; }

/* ── 独立搜索页 ── */
.search-page { max-width: 860px; }
.search-page-form {
    display: flex;
    gap: 8px;
    margin: 16px 0 12px;
}
.search-page-input {
    flex: 1;
    padding: 8px 14px;
    border: 1px solid var(--border);
    border-radius: 20px;
    background: var(--bg);
    color: var(--text);
    font-size: 0.95em;
    outline: none;
    transition: border-color 0.2s, box-shadow 0.2s;
}
.search-page-input:focus {
    border-color: var(--primary);
    box-shadow: 0 0 0 2px var(--primary-light);
}
.search-page-submit {
    padding: 8px 20px;
    border-radius: 20px;
    border: none;
    background: var(--primary);
    color: #fff;
    font-size: 0.9em;
    cursor: pointer;
    transition: opacity 0.2s;
}
.search-page-submit:hover { opacity: 0.9; }
.search-page-meta { margin-bottom: 12px; color: var(--text-secondary); font-size: 0.85em; }
.search-result-card {
    padding: 14px 0;
    border-bottom: 1px solid var(--border);
}
.search-result-card a {
    text-decoration: none;
    color: var(--primary);
    font-size: 1.05em;
    font-weight: 600;
}
.search-result-card a:hover { text-decoration: underline; }
.search-result-snippet {
    margin-top: 6px;
    font-size: 0.9em;
    color: var(--text-secondary);
    line-height: 1.5;
}
.search-result-meta {
    font-size: 0.78em;
    color: var(--text-secondary);
    margin-top: 4px;
}
.search-results-list mark {
    background: #ffeaa7;
    color: inherit;
    border-radius: 2px;
    padding: 0 1px;
}
[data-theme="dark"] .search-results-list mark { background: #b7791f; }

@media (max-width: 900px) {
    .search-page-form { flex-wrap: wrap; }
    .search-page-input { width: 100%; }
}

/* ── 选择题互动练习 ── */
.choice-quiz {
    margin: 10px 0;
    padding: 10px;
    background: var(--code-bg);
    border-radius: 8px;
    border: 1px solid var(--border);
}
.choice-options {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    margin-bottom: 10px;
}
.choice-btn {
    padding: 6px 14px;
    border: 1px solid var(--border);
    border-radius: 18px;
    background: var(--bg);
    color: var(--text);
    font-size: 0.85em;
    cursor: pointer;
    transition: all 0.15s;
    user-select: none;
}
.choice-btn:hover {
    border-color: var(--primary);
    color: var(--primary);
}
.choice-btn.selected {
    background: var(--primary);
    color: #fff;
    border-color: var(--primary);
}
.quiz-actions {
    display: flex;
    gap: 8px;
}
.quiz-actions button {
    padding: 5px 14px;
    border: 1px solid var(--accent);
    border-radius: 16px;
    background: var(--accent);
    color: #fff;
    font-size: 0.82em;
    cursor: pointer;
    transition: opacity 0.15s;
}
.quiz-actions button:hover { opacity: 0.85; }
.quiz-feedback {
    margin-top: 8px;
    font-size: 0.88em;
    font-weight: 600;
    min-height: 1.2em;
}
.quiz-feedback.correct { color: var(--accent); }
.quiz-feedback.wrong { color: #e74c3c; }
[data-theme="dark"] .quiz-feedback.wrong { color: #ff7675; }

/* ── 词汇组句互动练习 ── */
.sentence-builder {
    margin: 10px 0;
    padding: 12px;
    background: var(--code-bg);
    border-radius: 10px;
    border: 1px solid var(--border);
}
.word-bank {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
    margin-bottom: 10px;
}
.word-btn {
    padding: 5px 12px;
    border: 1px solid var(--primary);
    border-radius: 16px;
    background: var(--bg);
    color: var(--primary);
    font-size: 0.88em;
    cursor: pointer;
    transition: all 0.15s;
    user-select: none;
}
.word-btn:hover:not(:disabled) {
    background: var(--primary);
    color: #fff;
}
.word-btn:disabled, .word-btn.used {
    opacity: 0.35;
    cursor: not-allowed;
    border-color: var(--border);
    color: var(--text-secondary);
}
.answer-area {
    min-height: 40px;
    padding: 8px 10px;
    background: var(--bg);
    border: 2px dashed var(--border);
    border-radius: 8px;
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
    align-items: center;
    margin-bottom: 10px;
}
.answer-area .placeholder {
    color: var(--text-secondary);
    font-size: 0.85em;
}
.word-chip {
    display: inline-block;
    padding: 4px 10px;
    background: var(--primary);
    color: #fff;
    border-radius: 14px;
    font-size: 0.85em;
    cursor: pointer;
    transition: opacity 0.15s;
}
.word-chip:hover { opacity: 0.8; }
.builder-actions {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
}
.builder-actions button {
    padding: 5px 14px;
    border: 1px solid var(--border);
    border-radius: 16px;
    background: var(--bg);
    color: var(--text);
    font-size: 0.82em;
    cursor: pointer;
    transition: all 0.15s;
}
.builder-actions button:hover {
    border-color: var(--primary);
    color: var(--primary);
}
.btn-check {
    background: var(--accent) !important;
    color: #fff !important;
    border-color: var(--accent) !important;
}
.btn-check:hover { opacity: 0.85; }
.builder-feedback {
    margin-top: 8px;
    font-size: 0.88em;
    font-weight: 600;
    min-height: 1.2em;
}
.builder-feedback.correct { color: var(--accent); }
.builder-feedback.wrong { color: #e74c3c; }
[data-theme="dark"] .builder-feedback.wrong { color: #ff7675; }