:root {
    --bg-dark: #0b0c10;
    --bg-card: rgba(30, 31, 41, 0.45);
    --border-glass: rgba(255, 255, 255, 0.08);
    --border-accent: rgba(255, 255, 255, 0.15);
    --text-primary: #f5f7fa;
    --text-secondary: #a0aec0;
    --text-muted: #718096;
    
    --color-listening: #00bfff;
    --color-structure: #9d4edd;
    --color-reading: #00f5d4;
    
    --color-success: #2ec4b6;
    --color-danger: #e63946;
    --color-gold: #ffb703;
    
    --font-sans: 'Outfit', 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
}

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

body {
    background-color: var(--bg-dark);
    color: var(--text-primary);
    font-family: var(--font-sans);
    min-height: 100vh;
    overflow-x: hidden;
    position: relative;
}

/* Background Glowing Spheres */
body::before, body::after {
    content: '';
    position: absolute;
    width: 400px;
    height: 400px;
    border-radius: 50%;
    filter: blur(150px);
    z-index: -1;
    opacity: 0.25;
    pointer-events: none;
}

body::before {
    background: radial-gradient(circle, var(--color-listening) 0%, transparent 70%);
    top: 10%;
    left: -100px;
}

body::after {
    background: radial-gradient(circle, var(--color-structure) 0%, transparent 70%);
    bottom: 10%;
    right: -100px;
}

/* Container & Navbar */
.app-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

.main-navbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px 25px;
    border-radius: 16px;
    background: var(--bg-card);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border: 1px solid var(--border-glass);
    box-shadow: 0 8px 32px 0 rgba(0, 0, 0, 0.3);
    margin-bottom: 30px;
}

.nav-brand {
    font-size: 1.4rem;
    font-weight: 800;
    letter-spacing: 1px;
    background: linear-gradient(135deg, var(--color-listening) 0%, var(--color-structure) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    display: flex;
    align-items: center;
    gap: 10px;
    text-decoration: none;
}

.nav-links {
    display: flex;
    gap: 15px;
}

.nav-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 500;
    font-size: 0.95rem;
    padding: 8px 16px;
    border-radius: 8px;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    gap: 8px;
}

.nav-link:hover, .nav-link.active {
    color: var(--text-primary);
    background: rgba(255, 255, 255, 0.05);
}

.nav-link.active {
    border-bottom: 2px solid var(--color-listening);
}

/* Glass Card styling */
.glass-panel {
    background: var(--bg-card);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border: 1px solid var(--border-glass);
    border-radius: 20px;
    padding: 25px;
    box-shadow: 0 8px 32px 0 rgba(0, 0, 0, 0.2);
}

/* Welcome Banner */
.welcome-banner {
    position: relative;
    overflow: hidden;
    padding: 35px;
    border-radius: 20px;
    background: linear-gradient(135deg, rgba(30, 31, 41, 0.8) 0%, rgba(10, 10, 15, 0.9) 100%);
    border: 1px solid var(--border-accent);
    margin-bottom: 35px;
}

.welcome-banner::before {
    content: '';
    position: absolute;
    top: -50%;
    right: -20%;
    width: 300px;
    height: 300px;
    background: radial-gradient(circle, rgba(157, 78, 221, 0.2) 0%, transparent 70%);
    z-index: 0;
    pointer-events: none;
}

.welcome-title {
    font-size: 1.8rem;
    font-weight: 700;
    margin-bottom: 10px;
    z-index: 1;
    position: relative;
}

.welcome-desc {
    color: var(--text-secondary);
    font-size: 0.95rem;
    line-height: 1.6;
    max-width: 700px;
    z-index: 1;
    position: relative;
}

/* Category Grid */
.categories-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 25px;
}

.category-card {
    position: relative;
    overflow: hidden;
    transition: transform 0.3s ease, border-color 0.3s ease;
}

.category-card:hover {
    transform: translateY(-5px);
}

.category-card.border-listening:hover { border-color: var(--color-listening); }
.category-card.border-structure:hover { border-color: var(--color-structure); }
.category-card.border-reading:hover { border-color: var(--color-reading); }

.category-glow {
    position: absolute;
    top: -100px;
    right: -100px;
    width: 200px;
    height: 200px;
    border-radius: 50%;
    filter: blur(80px);
    z-index: 0;
    pointer-events: none;
    opacity: 0.15;
}

.glow-listening { background-color: var(--color-listening); }
.glow-structure { background-color: var(--color-structure); }
.glow-reading { background-color: var(--color-reading); }

.category-icon-box {
    width: 50px;
    height: 50px;
    border-radius: 12px;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.5rem;
    margin-bottom: 20px;
    color: var(--text-primary);
}

.bg-listening { background: linear-gradient(135deg, #0077b6, var(--color-listening)); }
.bg-structure { background: linear-gradient(135deg, #5a189a, var(--color-structure)); }
.bg-reading { background: linear-gradient(135deg, #00b4d8, var(--color-reading)); }

.category-name {
    font-size: 1.3rem;
    font-weight: 700;
    margin-bottom: 8px;
}

.category-desc {
    color: var(--text-secondary);
    font-size: 0.88rem;
    line-height: 1.5;
    margin-bottom: 20px;
}

.category-progress-text {
    font-size: 0.85rem;
    color: var(--text-secondary);
    display: flex;
    justify-content: space-between;
    margin-bottom: 8px;
}

.category-progress-text span {
    font-weight: 600;
    color: var(--text-primary);
}

.progress-bar-container {
    width: 100%;
    height: 8px;
    background: rgba(255, 255, 255, 0.05);
    border-radius: 10px;
    overflow: hidden;
    margin-bottom: 20px;
}

.progress-bar {
    height: 100%;
    border-radius: 10px;
    transition: width 0.5s ease;
}

.bg-listening { background-color: var(--color-listening); }
.bg-structure { background-color: var(--color-structure); }
.bg-reading { background-color: var(--color-reading); }

.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 10px 20px;
    border-radius: 10px;
    font-weight: 600;
    font-size: 0.9rem;
    text-decoration: none;
    cursor: pointer;
    transition: all 0.3s ease;
    border: none;
    color: #fff;
}

.btn-listening { background: var(--color-listening); }
.btn-listening:hover { background: #009ad4; box-shadow: 0 0 15px rgba(0, 191, 255, 0.4); }
.btn-structure { background: var(--color-structure); }
.btn-structure:hover { background: #7b2cbf; box-shadow: 0 0 15px rgba(157, 78, 221, 0.4); }
.btn-reading { background: var(--color-reading); }
.btn-reading:hover { background: #00d2b4; box-shadow: 0 0 15px rgba(0, 245, 212, 0.4); }

.btn-secondary {
    background: rgba(255, 255, 255, 0.08);
    color: var(--text-primary);
    border: 1px solid var(--border-glass);
}
.btn-secondary:hover {
    background: rgba(255, 255, 255, 0.15);
}

/* Quiz Page Layout */
.quiz-header-bar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px 25px;
    margin-bottom: 25px;
    border-radius: 16px;
}

.btn-back {
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 500;
    font-size: 0.9rem;
    display: inline-flex;
    align-items: center;
    gap: 8px;
    transition: color 0.2s ease;
}
.btn-back:hover {
    color: var(--text-primary);
}

.category-indicator {
    padding: 4px 12px;
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.quiz-container {
    display: grid;
    grid-template-columns: 1fr;
    gap: 25px;
}

.quiz-question-box {
    margin-bottom: 25px;
}

.quiz-passage-header {
    font-size: 1rem;
    font-weight: 700;
    color: var(--text-secondary);
    margin-bottom: 10px;
    border-bottom: 1px solid var(--border-glass);
    padding-bottom: 10px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.quiz-passage-body {
    background: rgba(0, 0, 0, 0.2);
    border: 1px solid var(--border-glass);
    border-radius: 12px;
    padding: 20px;
    font-size: 1.05rem;
    line-height: 1.65;
    color: var(--text-secondary);
    text-align: justify;
    margin-bottom: 20px;
    max-height: 350px;
    overflow-y: auto;
}

.quiz-question-text {
    font-size: 1.2rem;
    font-weight: 600;
    line-height: 1.5;
    margin-bottom: 25px;
}

/* Audio Player CSS */
.audio-player-panel {
    display: flex;
    align-items: center;
    gap: 15px;
    background: rgba(0, 191, 255, 0.08);
    border: 1px solid rgba(0, 191, 255, 0.2);
    border-radius: 12px;
    padding: 15px 20px;
    margin-bottom: 25px;
}

.btn-play-audio {
    width: 45px;
    height: 45px;
    border-radius: 50%;
    background: var(--color-listening);
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.2rem;
    color: #fff;
    cursor: pointer;
    border: none;
    transition: all 0.3s ease;
}
.btn-play-audio:hover {
    transform: scale(1.08);
    box-shadow: 0 0 10px rgba(0, 191, 255, 0.4);
}

.audio-status-text {
    font-size: 0.88rem;
    color: var(--text-secondary);
    font-weight: 500;
}

.tts-speaker-tag {
    font-size: 0.72rem;
    padding: 2px 6px;
    border-radius: 4px;
    background: rgba(255, 255, 255, 0.1);
    color: var(--text-primary);
    margin-right: 5px;
    font-weight: 600;
}

/* Side-by-side reading layout */
.reading-split-workspace {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 25px;
}

@media (max-width: 850px) {
    .reading-split-workspace {
        grid-template-columns: 1fr;
    }
}

/* Options Stack */
.options-stack {
    display: flex;
    flex-direction: column;
    gap: 12px;
    margin-bottom: 25px;
}

.option-item {
    display: flex;
    align-items: center;
    padding: 15px 20px;
    border-radius: 12px;
    background: rgba(255, 255, 255, 0.03);
    border: 1px solid var(--border-glass);
    cursor: pointer;
    transition: all 0.25s ease;
    text-align: left;
    width: 100%;
    color: var(--text-primary);
    font-size: 0.95rem;
    line-height: 1.4;
}

.option-item:hover:not(.disabled) {
    background: rgba(255, 255, 255, 0.08);
    border-color: var(--border-accent);
}

.option-badge {
    width: 28px;
    height: 28px;
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
    background: rgba(255, 255, 255, 0.08);
    font-weight: 700;
    font-size: 0.85rem;
    margin-right: 15px;
    flex-shrink: 0;
    transition: all 0.2s ease;
}

.option-item.selected {
    background: rgba(0, 191, 255, 0.1);
    border-color: var(--color-listening);
}
.option-item.selected .option-badge {
    background: var(--color-listening);
    color: #fff;
}

.option-item.correct {
    background: rgba(46, 196, 182, 0.15) !important;
    border-color: var(--color-success) !important;
}
.option-item.correct .option-badge {
    background: var(--color-success) !important;
    color: #fff !important;
}

.option-item.wrong {
    background: rgba(230, 57, 70, 0.15) !important;
    border-color: var(--color-danger) !important;
}
.option-item.wrong .option-badge {
    background: var(--color-danger) !important;
    color: #fff !important;
}

/* Written Expression Spans */
.written-expression-container {
    font-size: 1.25rem;
    line-height: 2.2;
    background: rgba(0,0,0,0.15);
    border: 1px solid var(--border-glass);
    border-radius: 12px;
    padding: 20px 25px;
    margin-bottom: 25px;
    color: var(--text-primary);
}

.written-option {
    cursor: pointer;
    display: inline-block;
    position: relative;
    padding: 2px 4px;
    margin: 0 4px;
    border-radius: 4px;
    transition: all 0.2s ease;
    user-select: none;
}
.written-option u {
    text-underline-offset: 4px;
    text-decoration-thickness: 2px;
}
.written-option:hover {
    background: rgba(255, 255, 255, 0.1);
}
.written-option.selected {
    background: rgba(157, 78, 221, 0.2);
    box-shadow: 0 0 0 1px var(--color-structure);
}
.written-option.correct {
    background: rgba(46, 196, 182, 0.2) !important;
    box-shadow: 0 0 0 1px var(--color-success) !important;
}
.written-option.wrong {
    background: rgba(230, 57, 70, 0.2) !important;
    box-shadow: 0 0 0 1px var(--color-danger) !important;
}

.option-label {
    font-size: 0.65rem;
    font-weight: 700;
    vertical-align: bottom;
    margin-left: 2px;
    opacity: 0.8;
    background: rgba(255, 255, 255, 0.15);
    padding: 1px 4px;
    border-radius: 3px;
    text-decoration: none !important;
    display: inline-block;
    line-height: 1;
}

/* Explanation Panel */
.explanation-panel {
    border-left: 4px solid var(--color-gold);
    background: rgba(255, 183, 3, 0.05);
    margin-top: 25px;
    border-radius: 0 12px 12px 0;
    overflow: hidden;
}

.explanation-header {
    padding: 15px 20px;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-weight: 700;
    font-size: 0.95rem;
    color: var(--color-gold);
}

.explanation-body {
    padding: 0 20px 20px 20px;
    font-size: 0.92rem;
    line-height: 1.6;
    color: var(--text-secondary);
    border-top: 1px solid rgba(255, 183, 3, 0.1);
    padding-top: 15px;
}

/* Baby Analogy Box */
.baby-box {
    background: rgba(255, 255, 255, 0.02);
    border: 1px dashed rgba(255, 255, 255, 0.15);
    border-radius: 12px;
    padding: 15px 20px;
    margin-bottom: 20px;
}
.baby-box-header {
    display: flex;
    align-items: center;
    gap: 8px;
    margin-bottom: 8px;
    color: var(--color-listening);
}
.baby-box-header h4 {
    font-weight: 700;
    font-size: 0.9rem;
}
.baby-box p {
    font-size: 0.88rem;
    line-height: 1.5;
    color: var(--text-secondary);
}

/* Formula & Tips Box */
.formula-box, .tips-box {
    border-radius: 12px;
    padding: 20px;
    margin-bottom: 20px;
}

.formula-box {
    background: rgba(0, 245, 212, 0.03);
    border: 1px solid rgba(0, 245, 212, 0.15);
}
.formula-box h4 {
    color: var(--color-reading);
    font-weight: 700;
    margin-bottom: 10px;
    font-size: 0.95rem;
}
.formula-box ul, .formula-box ol {
    margin-left: 20px;
    font-size: 0.88rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

.tips-box {
    background: rgba(255, 183, 3, 0.03);
    border: 1px solid rgba(255, 183, 3, 0.15);
}
.tips-box h4 {
    color: var(--color-gold);
    font-weight: 700;
    margin-bottom: 10px;
    font-size: 0.95rem;
}
.tips-box p {
    font-size: 0.88rem;
    color: var(--text-secondary);
    line-height: 1.5;
}

/* Academy Modules Workspace */
.module-workspace {
    display: grid;
    grid-template-columns: 280px 1fr;
    gap: 25px;
}

@media (max-width: 800px) {
    .module-workspace {
        grid-template-columns: 1fr;
    }
}

.module-sidebar {
    padding: 20px;
    height: fit-content;
}

.sidebar-title {
    font-size: 1.1rem;
    font-weight: 700;
    margin-bottom: 20px;
    border-bottom: 1px solid var(--border-glass);
    padding-bottom: 10px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.chapters-list {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.chapter-item {
    display: flex;
    align-items: center;
    padding: 10px 15px;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s ease;
    font-size: 0.88rem;
    color: var(--text-secondary);
}

.chapter-item:hover, .chapter-item.active {
    background: rgba(255, 255, 255, 0.05);
    color: var(--text-primary);
}

.chapter-item.active {
    border-left: 3px solid var(--color-listening);
    font-weight: 600;
}

.chapter-num {
    width: 22px;
    height: 22px;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.08);
    display: flex;
    justify-content: center;
    align-items: center;
    font-weight: 700;
    font-size: 0.75rem;
    margin-right: 12px;
    flex-shrink: 0;
}

.chapter-item.active .chapter-num {
    background: var(--color-listening);
    color: #fff;
}

.chapter-content {
    display: none;
}

.chapter-content.active {
    display: block;
    animation: fadeIn 0.4s ease forwards;
}

.lesson-title {
    font-size: 1.6rem;
    font-weight: 700;
    margin-bottom: 10px;
}

.lesson-intro {
    color: var(--text-secondary);
    font-size: 0.95rem;
    margin-bottom: 25px;
    line-height: 1.5;
}

/* History / Stat list */
.visual-table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 15px;
}

.visual-table th, .visual-table td {
    padding: 12px 15px;
    text-align: left;
    border-bottom: 1px solid var(--border-glass);
    font-size: 0.88rem;
}

.visual-table th {
    font-weight: 700;
    color: var(--text-secondary);
    background: rgba(255, 255, 255, 0.02);
}

/* Animations */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.fade-in {
    animation: fadeIn 0.5s ease forwards;
}

.code-box {
    display: block;
    background: rgba(0, 0, 0, 0.4);
    border: 1px solid var(--border-glass);
    border-radius: 8px;
    padding: 15px;
    font-family: 'Courier New', Courier, monospace;
    font-size: 0.88rem;
    color: #00f5d4;
    overflow-x: auto;
    margin-bottom: 20px;
    line-height: 1.5;
}

/* Float circular chart stats */
.circular-progress {
    position: relative;
    width: 80px;
    height: 80px;
    border-radius: 50%;
    background: conic-gradient(var(--color-listening) calc(var(--percent) * 1%), rgba(255, 255, 255, 0.05) 0);
    display: flex;
    justify-content: center;
    align-items: center;
    flex-shrink: 0;
}

.circular-progress::before {
    content: '';
    position: absolute;
    width: 68px;
    height: 68px;
    border-radius: 50%;
    background: #1e1f29;
}

.circular-value {
    position: relative;
    font-size: 0.95rem;
    font-weight: 700;
}

/* =============================================
   KARAOKE SUBTITLE & AUDIO DURATION STYLES
   ============================================= */

/* Audio duration badge */
.audio-duration-badge {
    display: inline-flex;
    align-items: center;
    gap: 5px;
    font-size: 0.72rem;
    font-weight: 600;
    color: var(--color-listening);
    background: rgba(0, 191, 255, 0.1);
    border: 1px solid rgba(0, 191, 255, 0.25);
    border-radius: 20px;
    padding: 3px 10px;
    margin-left: 8px;
    letter-spacing: 0.3px;
    flex-shrink: 0;
}

.audio-duration-badge i {
    font-size: 0.68rem;
}

/* Karaoke subtitle box wrapper */
.karaoke-subtitle-box {
    margin-top: 14px;
    background: rgba(0, 0, 0, 0.25);
    border: 1px solid rgba(0, 191, 255, 0.15);
    border-radius: 12px;
    padding: 14px 18px;
    max-height: 220px;
    overflow-y: auto;
    scroll-behavior: smooth;
    display: none; /* shown via JS */
}

.karaoke-subtitle-box.visible {
    display: block;
}

/* Individual subtitle line */
.subtitle-line {
    display: flex;
    align-items: flex-start;
    gap: 10px;
    padding: 8px 10px;
    border-radius: 8px;
    margin-bottom: 4px;
    transition: all 0.35s ease;
    opacity: 0.6;
    border-left: 3px solid transparent;
}

/* State: Not yet read */
.subtitle-line.unread {
    opacity: 0.6;
}

/* State: Currently being spoken (karaoke active line) */
.subtitle-line.speaking {
    opacity: 1;
    background: rgba(0, 191, 255, 0.15);
    border-left-color: var(--color-listening);
    animation: karaokePulse 0.5s ease;
}

/* State: Already spoken */
.subtitle-line.spoken {
    opacity: 0.8;
    border-left-color: rgba(255, 255, 255, 0.15);
}

@keyframes karaokePulse {
    0%   { transform: scale(1); }
    30%  { transform: scale(1.01); }
    100% { transform: scale(1); }
}

/* Speaker name tag inside karaoke line */
.subtitle-speaker-tag {
    display: inline-block;
    font-size: 0.7rem;
    font-weight: 700;
    padding: 2px 7px;
    border-radius: 4px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    flex-shrink: 0;
    margin-top: 1px;
    white-space: nowrap;
}

.subtitle-speaker-tag.tag-woman   { background: rgba(255, 100, 200, 0.15); color: #ff80e5; }
.subtitle-speaker-tag.tag-man     { background: rgba(100, 180, 255, 0.15); color: #80c8ff; }
.subtitle-speaker-tag.tag-narrator{ background: rgba(255, 200, 100, 0.15); color: #ffcc60; }
.subtitle-speaker-tag.tag-professor{ background: rgba(160, 100, 255, 0.15); color: #bf80ff; }

/* Subtitle line text */
.subtitle-line-text {
    font-size: 0.88rem;
    line-height: 1.5;
    color: var(--text-secondary);
    flex: 1;
}

.subtitle-line.speaking .subtitle-line-text {
    color: var(--text-primary);
    font-weight: 500;
}

/* Audio player expanded layout */
.audio-player-panel {
    flex-direction: column;
    align-items: stretch !important;
}

.audio-player-top-row {
    display: flex;
    align-items: center;
    gap: 15px;
    width: 100%;
    justify-content: space-between;
}

.audio-player-left {
    display: flex;
    align-items: center;
    gap: 15px;
    flex: 1;
}

.audio-player-meta {
    display: flex;
    flex-direction: column;
    gap: 4px;
}

/* Subtitle completed banner (shown after audio finishes) */
.subtitle-completed-notice {
    display: none;
    font-size: 0.78rem;
    color: var(--color-success);
    margin-top: 8px;
    display: none;
    align-items: center;
    gap: 6px;
}

.subtitle-completed-notice.visible {
    display: flex;
}

/* Karaoke Word-by-Word Highlight */
.word-token {
    display: inline-block;
    transition: opacity 0.15s ease, color 0.15s ease;
}

/* Default state for words in the active speaking line (unread) */
.subtitle-line.speaking .word-token {
    opacity: 0.4;
}

/* Currently active word being spoken */
.subtitle-line.speaking .word-token.word-active {
    opacity: 1 !important;
    color: var(--color-listening) !important;
    font-weight: 700;
}

/* Words that have already been spoken in the active line */
.subtitle-line.speaking .word-token.word-past {
    opacity: 1;
    color: var(--text-primary) !important;
}