:root {
    /* Base Variables (Light Mode Defaults) */
    --accent-gold: #ffc107;
    --text-dark: #333;
    --text-light: #666;
    --bg-light: #f8f9fa;
    --white: #ffffff;
    --shadow-sm: 0 4px 6px rgba(0,0,0,0.05);
    --shadow-md: 0 10px 15px rgba(0,0,0,0.1);
    
    /* Default Color (Red) */
    --theme-primary: #d32f2f;
    --theme-primary-dark: #b71c1c;
    --theme-bg-alpha: rgba(211, 47, 47, 0.1);

    --font-ui: 'Poppins', 'Segoe UI', Tahoma, sans-serif;
    /* Use Songti / SimSun for academic Chinese look, fallback to modern Sans if unavailable */
    --font-cn: 'Songti SC', 'SimSun', 'STSong', 'Noto Serif SC', 'Times New Roman', serif;
}

/* --- Color Schemes --- */

/* Red (Default) - Explicitly defined for consistency */
[data-color="red"] {
    --theme-primary: #d32f2f;
    --theme-primary-dark: #b71c1c;
    --theme-bg-alpha: rgba(211, 47, 47, 0.1);
}

/* Blue */
[data-color="blue"] {
    --theme-primary: #1976d2;
    --theme-primary-dark: #0d47a1;
    --theme-bg-alpha: rgba(25, 118, 210, 0.1);
}

/* Green */
[data-color="green"] {
    --theme-primary: #388e3c;
    --theme-primary-dark: #1b5e20;
    --theme-bg-alpha: rgba(56, 142, 60, 0.1);
}

/* Purple */
[data-color="purple"] {
    --theme-primary: #9c27b0;
    --theme-primary-dark: #7b1fa2;
    --theme-bg-alpha: rgba(156, 39, 176, 0.1);
}

/* Yollow */
[data-color="yollow"] {
    --theme-primary: #f9a825;
    --theme-primary-dark: #f57f17;
    --theme-bg-alpha: rgba(249, 168, 37, 0.12);
}

/* White (Monochrome/Gray) */
[data-color="white"] {
    --theme-primary: #607d8b;
    --theme-primary-dark: #455a64;
    --theme-bg-alpha: rgba(96, 125, 139, 0.1);
}

/* --- Modes (Light / Dark) --- */

/* Dark Mode Overrides */
[data-mode="dark"] {
    --bg-light: #121212;
    --white: #1e1e1e;
    --text-dark: #e0e0e0;
    --text-light: #b0b0b0;
    --shadow-sm: 0 4px 6px rgba(0,0,0,0.3);
    --shadow-md: 0 10px 15px rgba(0,0,0,0.5);
}

/* Adjust primary colors for dark mode to ensure contrast if needed */
/* For now, we will rely on the standard colors, but we can tweak them here like:
[data-mode="dark"][data-color="blue"] { --theme-primary: #90caf9; } 
*/

* {
    box-sizing: border-box;
}

body {
    font-family: var(--font-ui);
    background-color: var(--bg-light);
    color: var(--text-dark);
    margin: 0;
    padding: 0;
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Theme Selector */
.theme-switch-wrapper {
    position: absolute;
    top: 20px;
    right: 20px;
    z-index: 100;
    display: flex;
    flex-direction: column; /* Stack the two groups */
    align-items: flex-end;
    gap: 10px;
}

.theme-group {
    display: flex;
    gap: 8px;
    background: rgba(255, 255, 255, 0.8);
    padding: 5px;
    border-radius: 20px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

[data-mode="dark"] .theme-group {
    background: rgba(30, 30, 30, 0.8);
}

.theme-btn {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    border: 2px solid rgba(0,0,0,0.1);
    cursor: pointer;
    transition: transform 0.2s;
}

.mode-btn {
    font-size: 12px;
    padding: 2px 8px;
    cursor: pointer;
    border-radius: 12px;
    border: 1px solid #ddd;
    background: #fff;
    color: #333;
}

.mode-btn.active {
    background: #333;
    color: #fff;
    border-color: #333;
}

[data-mode="dark"] .mode-btn {
    background: #333;
    color: #ccc;
    border-color: #555;
}

[data-mode="dark"] .mode-btn.active {
    background: #f1f1f1;
    color: #333;
}

.theme-btn:hover {
    transform: scale(1.2);
}

.theme-btn.active {
    border-color: var(--text-dark); /* Show active border based on mode */
    transform: scale(1.2);
    box-shadow: 0 0 0 2px var(--bg-light); /* Double ring effect */
}

/* Hero Section */
.hero {
    background: linear-gradient(135deg, var(--theme-primary) 0%, var(--theme-primary-dark) 100%);
    color: var(--white); /* For dark mode, white text is usually fine on colored bg, but be careful */
    padding: 5rem 1rem;
    text-align: center;
    clip-path: polygon(0 0, 100% 0, 100% 85%, 0 100%);
    margin-bottom: 2rem;
    transition: background 0.5s ease;
}

[data-theme="dark"] .hero {
    /* Adjust hero for dark mode if needed, or keep colored gradient */
    color: #121212; /* Dark text on light blue gradient looks better */
}

.hero h1 {
    font-size: 3.5rem;
    margin: 0 0 10px 0;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.2);
}

.hero .tagline {
    font-size: 1.5rem;
    font-weight: 300;
    margin-bottom: 1rem;
    opacity: 0.9;
}

.hero-desc {
    max-width: 600px;
    margin: 0 auto;
    opacity: 0.8;
}

/* Introduction */
.intro {
    text-align: center;
    margin-bottom: 3rem;
}

.intro h2 {
    font-size: 2rem;
    color: var(--text-dark);
    margin-bottom: 0.5rem;
}

.intro p {
    color: var(--text-light);
}

/* Grid Layout */
.level-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    padding-bottom: 4rem;
}

/* Cards */
.level-card {
    background-color: var(--white);
    border-radius: 16px;
    padding: 2rem;
    text-align: center;
    text-decoration: none;
    color: var(--text-dark);
    transition: transform 0.3s ease, box-shadow 0.3s ease, background-color 0.3s, color 0.3s;
    box-shadow: var(--shadow-sm);
    border: 1px solid rgba(0,0,0,0.05);
    display: flex;
    flex-direction: column;
    align-items: center;
    position: relative;
    overflow: hidden;
}

.level-card:hover {
    transform: translateY(-10px);
    box-shadow: var(--shadow-md);
}

.card-icon {
    width: 60px;
    height: 60px;
    background-color: var(--theme-bg-alpha);
    color: var(--theme-primary);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.8rem;
    font-weight: bold;
    margin-bottom: 1rem;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.level-card:hover .card-icon {
    background-color: var(--theme-primary);
    color: var(--white);
}
[data-theme="dark"] .level-card:hover .card-icon {
    color: #121212;
}

.level-card h3 {
    margin: 0.5rem 0;
    font-size: 1.5rem;
}

.level-card p {
    color: var(--text-light);
    margin: 0 0 1.5rem 0;
}

.card-link {
    color: var(--theme-primary);
    font-weight: 600;
    font-size: 0.9rem;
    margin-top: auto;
}

/* Footer */
footer {
    background-color: #333;
    color: #aaa;
    text-align: center;
    padding: 2rem 0;
    font-size: 0.9rem;
    margin-top: auto;
}

/* Previous Table Styles (Preserved) */
table {
    width: 100%; /* Changed to full width within container */
    max-width: 100%;
    margin: 2rem auto;
    border-collapse: separate; /* Required for sticky + border radius interaction */
    border-spacing: 0;
    background-color: var(--white);
    color: var(--text-dark);
    box-shadow: var(--shadow-md);
    border-radius: 8px;
}

thead {
    background-color: var(--theme-primary);
    color: var(--white);
}

th, td {
    padding: 15px;
    text-align: left;
    border-bottom: 1px solid rgba(0,0,0,0.1);
}

th {
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    position: sticky;
    top: 0;
    z-index: 100;
    background-color: var(--theme-primary); /* Ensure opacity when scrolling */
    color: var(--white);
    box-shadow: 0 2px 4px rgba(0,0,0,0.1); /* Optional: adds a subtle shadow to separate header */
}

th:first-child {
    border-top-left-radius: 8px;
}

th:last-child {
    border-top-right-radius: 8px;
}

thead tr:first-child th {
    /* Ensure radius is applied to the sticky elements top corners */
}

tbody tr:last-of-type td:first-child {
    border-bottom-left-radius: 8px;
}

tbody tr:last-of-type td:last-child {
    border-bottom-right-radius: 8px;
}

tbody tr:hover {
    background-color: rgba(0,0,0,0.02);
}

tbody tr:last-of-type td {
    border-bottom: 2px solid var(--theme-primary);
}

/* Responsive Table */
@media (max-width: 600px) {
    .hero h1 {
        font-size: 2.5rem;
    }
    
    th, td {
        padding: 10px;
        font-size: 0.9rem;
    }
}

/* Sentence Block Styles */
.sentence-block {
    min-width: 200px; /* Ensure column doesn't collapse too much */
    font-size: 0.9rem;
    line-height: 1.4;
}
.sentence-block .cn {
    font-family: var(--font-cn);
    font-size: 1.05rem;
    color: var(--text-dark);
    margin-bottom: 2px;
}
.sentence-block .py {
    color: var(--theme-primary);
    font-size: 0.85rem;
    margin-bottom: 2px;
}
.sentence-block .en {
    color: var(--text-light);
    font-size: 0.85rem;
    font-style: italic;
}
.hanzi-main {
    font-family: var(--font-cn);
    font-size: 1.4rem;
    font-weight: normal;
    -webkit-font-smoothing: none;
    -moz-osx-font-smoothing: grayscale;
}
/* Chapter Header in Table */
.chapter-header td {
    background-color: var(--theme-bg-alpha);
    color: var(--theme-primary-dark);
    font-weight: 700;
    text-align: center;
    font-size: 1.1rem;
    padding: 15px;
    border-top: 2px solid var(--theme-primary);
}

/* Chapter Header Interactive */
.chapter-header {
    -webkit-user-select: none; /* Chrome/Safari/Opera */
    -moz-user-select: none;    /* Firefox */
    -ms-user-select: none;     /* Internet Explorer/Edge */
    user-select: none;         /* Standard */
}
.chapter-header:hover {
    filter: brightness(0.95);
}
.chapter-header.open {
    border-bottom: 2px solid var(--theme-primary);
}

/* Back to Top Button (Webpage) */
#back-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    display: none; /* Hidden by default */
    background-color: var(--theme-primary);
    color: var(--white);
    border: none;
    outline: none;
    cursor: pointer;
    width: 50px;
    height: 50px;
    line-height: 50px; /* Center content vertically */
    text-align: center; /* Center content horizontally */
    padding: 0;
    border-radius: 50%;
    font-size: 24px;
    box-shadow: 0 4px 10px rgba(0,0,0,0.2);
    transition: background-color 0.3s, transform 0.3s;
    z-index: 1000;
}

#back-to-top:hover {
    background-color: var(--theme-primary-dark);
    transform: translateY(-5px);
}

/* Chapter Footer (Scroll to Chapter Top) */
.chapter-footer td {
    text-align: center;
    padding: 10px;
    border-top: 1px dashed rgba(0,0,0,0.1);
    background-color: rgba(0,0,0,0.01);
}

.chapter-top-btn {
    background: none;
    border: none;
    color: var(--theme-primary);
    cursor: pointer;
    font-size: 0.9rem;
    padding: 5px 15px;
    border-radius: 20px;
    border: 1px solid var(--theme-primary);
    transition: all 0.2s;
}

.chapter-top-btn:hover {
    background-color: var(--theme-primary);
    color: var(--white);
}


/* Audio Highlight */
.sentence-card.highlight-playing {
    background-color: #fff9c4; /* Light Yellow */
    border-color: var(--accent-gold);
    box-shadow: 0 0 10px rgba(255, 193, 7, 0.3);
    transform: scale(1.02);
    transition: all 0.3s ease;
}
[data-theme='dark'] .sentence-card.highlight-playing {
    background-color: rgba(255, 193, 7, 0.15);
    border-color: var(--accent-gold);
}

/* Audio Button */
.audio-btn {
    background: none;
    border: 2px solid var(--theme-primary);
    color: var(--theme-primary);
    border-radius: 50%;
    width: 36px;
    height: 36px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    margin-left: 10px;
    vertical-align: middle;
    transition: all 0.2s;
    font-size: 1rem;
}

.audio-btn:hover {
    background-color: var(--theme-primary);
    color: var(--white);
    transform: scale(1.1);
}

.audio-btn.playing {
    background-color: var(--theme-primary);
    color: var(--white);
    /* Simple Pulse Effect using box-shadow directly */
    box-shadow: 0 0 0 3px rgba(0,0,0,0.1); 
    border-color: transparent;
}


/* Coming Soon / Locked Levels */
.level-card.coming-soon {
    position: relative;
    cursor: not-allowed;
    background: #fdfdfd;
    border-color: #eee;
    overflow: hidden;
}

.level-card.coming-soon::after {
    content: '🚧 Under Construction';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%) rotate(-10deg);
    background: var(--theme-primary);
    color: var(--white);
    padding: 10px 20px;
    font-weight: bold;
    font-size: 1.2rem;
    white-space: nowrap;
    box-shadow: 0 4px 15px rgba(0,0,0,0.2);
    border: 2px dashed rgba(255,255,255,0.5);
    z-index: 10;
    border-radius: 8px;
    opacity: 0.95;
    transition: all 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.level-card.coming-soon:hover::after {
    transform: translate(-50%, -50%) rotate(0deg) scale(1.1);
}

.level-card.coming-soon .card-icon,
.level-card.coming-soon h3,
.level-card.coming-soon p,
.level-card.coming-soon .card-link {
    opacity: 0.3;
    filter: blur(1px);
    pointer-events: none;
}

.level-card.coming-soon:hover {
    transform: none;
    box-shadow: var(--shadow-sm);
}


/* Report Flag */
.report-btn {
    opacity: 0.2;
    cursor: pointer;
    font-size: 0.9rem;
    margin-left: 8px;
    background: none;
    border: none;
    color: #d32f2f; /* Red by default for alert */
    transition: opacity 0.2s;
}

tr:hover .report-btn,
.sentence-card:hover .report-btn,
.level-card:hover .report-btn {
    opacity: 1;
}

.report-btn:hover {
    transform: scale(1.2);
    opacity: 1;
}


/* Column Visibility Toggles */
.toggle-icon {
    font-size: 0.8em;
    margin-left: 5px;
    opacity: 0.7;
}

/* Masking Styles */
table.hide-hanzi .col-hanzi .hanzi-main,
table.hide-pinyin .col-pinyin,
table.hide-meaning .col-meaning,
table.hide-type .col-type,
table.hide-sentence .col-sentence {
    color: transparent !important;
    text-shadow: 0 0 10px var(--text-light);
    -webkit-user-select: none;
    user-select: none;
    transition: all 0.3s ease;
}

/* Special blur color for Hanzi */
table.hide-hanzi .col-hanzi .hanzi-main {
    text-shadow: 0 0 10px var(--theme-primary);
}

/* Reveal on hover */
table.hide-hanzi .col-hanzi:hover .hanzi-main,
table.hide-pinyin .col-pinyin:hover,
table.hide-meaning .col-meaning:hover,
table.hide-type .col-type:hover,
table.hide-sentence .col-sentence:hover {
    color: inherit !important;
    text-shadow: none;
    cursor: help;
}


th:hover {
    background-color: var(--theme-primary-dark);
    transition: background-color 0.2s ease;
}


/* Creative Footer Link */
.github-link {
    display: inline-flex;
    align-items: center;
    gap: 8px; /* Support for gap in flexbox for older browsers */
    margin-top: 15px;
    color: #bbb;
    text-decoration: none;
    background: rgba(255, 255, 255, 0.05);
    padding: 8px 16px;
    border-radius: 20px;
    -webkit-transition: all 0.3s ease;
    transition: all 0.3s ease;
    border: 1px solid rgba(255, 255, 255, 0.1);
    font-size: 0.85rem;

}

.github-link:hover {
    background: var(--theme-primary);
    border-color: var(--theme-primary);
    transform: translateY(-3px);
    box-shadow: 0 5px 15px rgba(0,0,0,0.3);
    color: #fff;
}

.github-icon {
    width: 18px;
    height: 18px;
    fill: currentColor;
}

/* Learned Row Styles */
.learned-row {
    background: linear-gradient(to right, rgba(76, 175, 80, 0.15), rgba(76, 175, 80, 0.05)) !important;
    border-left: 3px solid #4caf50;
    transition: all 0.3s ease;
}

[data-mode="dark"] .learned-row {
    background: linear-gradient(to right, rgba(76, 175, 80, 0.25), rgba(76, 175, 80, 0.1)) !important;
}

/* Unit Header Styles */
.unit-header-row {
    background-color: var(--theme-bg-alpha);
    border-bottom: 1px solid rgba(0,0,0,0.05); /* Softer border */
    position: relative;
    transition: background-color 0.2s;
}
.unit-header-row:hover {
    background-color: var(--theme-bg-alpha-hover, rgba(0,0,0,0.05));
}

.unit-header-title {
    padding: 15px; 
    font-weight: bold; 
    font-size: 1.2rem; 
    color: var(--theme-primary-dark);
}

/* Lesson Header Styles */
.lesson-header-row {
    background-color: rgba(255,255,255,0.02);
}

.lesson-header-cell {
    padding-left: 20px;
    border-left: 3px solid var(--theme-bg-alpha); /* Use the transparent theme color */
    color: var(--text-dark);
    font-weight: 500;
}

/* Checkbox Styles */
.learned-checkbox,
.unit-checkbox,
.chapter-checkbox,
[class*="lesson-checkbox-"],
#vocab-body input[type="checkbox"] {
    width: 18px;
    height: 18px;
    cursor: pointer;
    accent-color: #4caf50 !important; /* Always green, forced override */
}

.learned-checkbox:hover,
.unit-checkbox:hover,
.chapter-checkbox:hover,
[class*="lesson-checkbox-"]:hover,
#vocab-body input[type="checkbox"]:hover {
    transform: scale(1.1);
}

/* ===== Universal Search ===== */

.search-container {
    position: relative;
    max-width: 500px;
    margin: 1.2rem auto 0;
}

#global-search {
    width: 100%;
    padding: 12px 18px;
    border: 2px solid rgba(255,255,255,0.4);
    border-radius: 30px;
    font-size: 1rem;
    font-family: var(--font-ui);
    background: rgba(255,255,255,0.15);
    color: #fff;
    outline: none;
    transition: all 0.3s ease;
}

#global-search::placeholder {
    color: rgba(255,255,255,0.7);
}

#global-search:focus {
    background: rgba(255,255,255,0.25);
    border-color: rgba(255,255,255,0.8);
    box-shadow: 0 0 15px rgba(255,255,255,0.15);
}

.search-results {
    display: none;
    position: absolute;
    max-height: 400px;
    overflow-y: auto;
    background: var(--white);
    border-radius: 12px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.2);
    z-index: 9999;
}

.search-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 12px 16px;
    text-decoration: none;
    color: var(--text-dark);
    border-bottom: 1px solid rgba(0,0,0,0.06);
    transition: background 0.15s;
    cursor: pointer;
}

.search-item:last-child {
    border-bottom: none;
}

.search-item:hover {
    background: var(--theme-bg-alpha);
}

.search-item.search-empty,
.search-item.search-loading {
    justify-content: center;
    color: var(--text-light);
    font-style: italic;
    cursor: default;
    padding: 20px 16px;
}

.search-hanzi {
    font-family: var(--font-cn);
    font-size: 1.3rem;
    min-width: 50px;
    text-align: center;
    flex-shrink: 0;
}

.search-pinyin {
    color: var(--theme-primary);
    font-size: 0.9rem;
    min-width: 70px;
    flex-shrink: 0;
}

.search-meaning {
    color: var(--text-light);
    font-size: 0.9rem;
    font-style: italic;
    flex: 1;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

.search-level {
    font-size: 0.7rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    background: var(--theme-bg-alpha);
    color: var(--theme-primary);
    padding: 3px 8px;
    border-radius: 10px;
    flex-shrink: 0;
}

.search-item mark {
    background: rgba(255, 235, 59, 0.4);
    color: inherit;
    border-radius: 2px;
    padding: 0 1px;
}

[data-mode="dark"] .search-item mark {
    background: rgba(255, 235, 59, 0.25);
}

/* Highlight animation for word row targeted from search */
@keyframes search-highlight-fade {
    0%   { background-color: rgba(255, 235, 59, 0.5); }
    100% { background-color: transparent; }
}

.search-highlight-row {
    animation: search-highlight-fade 2.5s ease forwards;
    outline: 2px solid var(--theme-primary);
    outline-offset: -2px;
}

/* Responsive */
@media (max-width: 600px) {
    .search-container {
        max-width: 90%;
    }

    .search-item {
        gap: 8px;
        padding: 10px 12px;
    }

    .search-hanzi {
        font-size: 1.1rem;
        min-width: 40px;
    }

    .search-pinyin,
    .search-meaning {
        font-size: 0.8rem;
    }
}