@import url('https://fonts.googleapis.com/css2?family=Be+Vietnam+Pro:wght@400;500;600;700&family=Inter:wght@400;500;600;700&display=swap');

:root {
    --bg-light: #F1F5F9; /* Less glaring background */
    --bg-dark: #0B1220;

    --primary: #3B82F6;
    --secondary: #06B6D4;
    --accent: #8B5CF6;
    --success: #22C55E;
    --error: #EF4444;

    --card-bg-light: rgba(255, 255, 255, 0.85); /* More opaque to reduce glare */
    --card-bg-dark: rgba(255, 255, 255, 0.05);
    
    --card-border-light: rgba(255, 255, 255, 0.15);
    --card-border-dark: rgba(255, 255, 255, 0.08);

    --text-primary-light: #0f172a;
    --text-secondary-light: #475569;
    --text-primary-dark: #f8fafc;
    --text-secondary-dark: #cbd5e1;

    --bg: var(--bg-light);
    --card-bg: var(--card-bg-light);
    --card-border: var(--card-border-light);
    --text-primary: var(--text-primary-light);
    --text-secondary: var(--text-secondary-light);
    
    --shadow-base: 0 10px 30px -10px rgba(0, 0, 0, 0.05);
    --shadow-hover: 0 20px 40px -10px rgba(0, 0, 0, 0.1);
    
    --font-vn: 'Be Vietnam Pro', sans-serif;
    --font-en: 'Inter', sans-serif;
}

:root[data-theme="dark"] {
    --bg: var(--bg-dark);
    --card-bg: var(--card-bg-dark);
    --card-border: var(--card-border-dark);
    --text-primary: var(--text-primary-dark);
    --text-secondary: var(--text-secondary-dark);
    --shadow-base: 0 10px 30px -10px rgba(0, 0, 0, 0.3);
    --shadow-hover: 0 20px 40px -10px rgba(0, 0, 0, 0.5);
}

* { box-sizing: border-box; margin: 0; padding: 0; -webkit-tap-highlight-color: transparent; }

body {
    background-color: var(--bg);
    color: var(--text-primary);
    font-family: var(--font-vn);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    padding: 100px 20px 40px 20px;
    overflow-x: hidden;
    position: relative;
    transition: background-color 0.5s ease, color 0.5s ease;
}

.bg-layer {
    position: fixed;
    top: 0; left: 0; width: 100vw; height: 100vh;
    z-index: -2;
    background: radial-gradient(circle at 0% 0%, rgba(59, 130, 246, 0.08), transparent 50%),
                radial-gradient(circle at 100% 0%, rgba(139, 92, 246, 0.08), transparent 50%),
                radial-gradient(circle at 100% 100%, rgba(6, 182, 212, 0.08), transparent 50%),
                radial-gradient(circle at 0% 100%, rgba(59, 130, 246, 0.08), transparent 50%);
    animation: mesh-rotate 25s linear infinite;
    transform-origin: center;
}

.noise-layer {
    position: fixed;
    top: 0; left: 0; width: 100vw; height: 100vh;
    z-index: -1;
    opacity: 0.3;
    pointer-events: none;
    background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noiseFilter'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.8' numOctaves='3' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noiseFilter)'/%3E%3C/svg%3E");
    mix-blend-mode: overlay;
}

[data-theme="dark"] .noise-layer { opacity: 0.15; }

@keyframes mesh-rotate {
    0% { filter: hue-rotate(0deg); }
    50% { filter: hue-rotate(30deg); }
    100% { filter: hue-rotate(0deg); }
}

.top-nav {
    position: fixed;
    top: 24px;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 95%;
    max-width: 1100px;
    padding: 12px 24px;
    background: var(--card-bg);
    backdrop-filter: blur(24px);
    -webkit-backdrop-filter: blur(24px);
    border: 1px solid var(--card-border);
    border-radius: 100px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.02);
    z-index: 10;
}

.nav-logo { font-weight: 700; font-size: 1.1rem; color: var(--primary); font-family: var(--font-en); }
.nav-actions { display: flex; align-items: center; }
.nav-actions button {
    background: transparent; border: none; color: var(--text-primary); font-family: var(--font-vn);
    font-weight: 600; cursor: pointer; opacity: 0.7; transition: opacity 0.2s; font-size: 0.95rem;
}
.nav-actions button:hover { opacity: 1; }

.nav-link-btn { background: none; border: none; font-size: 1rem; font-weight: 600; color: var(--text-secondary); cursor: pointer; transition: 0.2s; font-family: var(--font-vn); user-select: none; padding: 8px 16px; border-radius: 100px; }
.nav-link-btn:hover { background: rgba(0,0,0,0.05); }
[data-theme="dark"] .nav-link-btn:hover { background: rgba(255,255,255,0.05); }
.nav-link-btn.active { color: var(--primary); background: rgba(59,130,246,0.1); }

.app-container {
    background: var(--card-bg);
    backdrop-filter: blur(24px);
    -webkit-backdrop-filter: blur(24px);
    border: 1px solid var(--card-border);
    border-radius: 32px;
    width: 100%;
    max-width: 800px; 
    min-height: 450px;
    padding: 48px;
    margin: auto;
    box-shadow: var(--shadow-base), inset 0 1px 0 rgba(255,255,255,0.1);
    position: relative;
    display: flex;
    flex-direction: column;
    transition: transform 0.4s ease, box-shadow 0.4s ease;
}
.app-container:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-hover), inset 0 1px 0 rgba(255,255,255,0.2);
}

.app-credit {
    margin-top: auto;
    padding-top: 48px;
    text-align: center;
    font-size: 0.85rem;
    color: var(--text-secondary);
    font-weight: 500;
    display: flex;
    justify-content: center;
    align-items: center;
    opacity: 0.7;
    transition: opacity 0.3s ease;
}
.app-credit:hover { opacity: 1; }

.screen { display: none; opacity: 0; width: 100%; }
.screen.active { display: flex; flex-direction: column; opacity: 1; animation: fadeIn 0.3s ease forwards; }
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }

h1 { font-size: 2rem; font-weight: 700; margin-bottom: 16px; line-height: 1.2; text-align: center; }
h2 { font-size: 1.15rem; font-weight: 500; margin-bottom: 32px; line-height: 1.5; white-space: pre-wrap; font-family: var(--font-en); }
p { font-size: 1rem; font-weight: 400; line-height: 1.6; color: var(--text-secondary); text-align: center; }
h3 { font-size: 1.1rem; font-weight: 600; }

.progress-container { display: flex; justify-content: flex-start; align-items: center; margin-bottom: 24px; flex-wrap: wrap; gap: 12px; }
.progress-capsule {
    display: inline-flex; align-items: center; background: rgba(0,0,0,0.04);
    border: 1px solid var(--card-border); padding: 8px 20px; border-radius: 100px;
    font-weight: 600; font-size: 0.95rem; color: var(--text-primary); overflow: hidden; position: relative;
}
[data-theme="dark"] .progress-capsule { background: rgba(255,255,255,0.04); }
.progress-capsule-bg {
    position: absolute; left: 0; top: 0; height: 100%;
    background: linear-gradient(90deg, rgba(59,130,246,0.1), rgba(59,130,246,0.3));
    z-index: 0; transition: width 0.4s ease-out;
}
.progress-capsule-text { position: relative; z-index: 1; }
.progress-score { margin-left: auto; font-weight: 700; color: var(--primary); font-size: 1.05rem; }

.timer-capsule.pulsing { animation: pulse-red 1s infinite alternate; }
@keyframes pulse-red {
    from { background: rgba(239, 68, 68, 0.1); color: var(--error); border-color: rgba(239,68,68,0.3); }
    to { background: rgba(239, 68, 68, 0.25); color: var(--error); border-color: rgba(239,68,68,0.6); }
}

.streak-banner {
    background: linear-gradient(90deg, var(--accent), var(--primary));
    color: white; font-weight: 600; padding: 6px 16px; border-radius: 12px;
    display: inline-block; margin: 0 auto 24px auto; text-align: center;
    box-shadow: 0 4px 15px rgba(139, 92, 246, 0.3);
    animation: pop-streak 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}
@keyframes pop-streak { 0% { transform: scale(0.5); opacity: 0; } 100% { transform: scale(1); opacity: 1; } }

.primary-btn {
    background: linear-gradient(135deg, var(--primary), var(--accent));
    color: white; border: none; padding: 14px 32px; border-radius: 100px;
    font-size: 1rem; font-weight: 600; cursor: pointer; min-height: 48px;
    transition: transform 0.2s cubic-bezier(0.175, 0.885, 0.32, 1.275), box-shadow 0.2s;
    margin: 24px auto 0; display: inline-block;
    box-shadow: 0 8px 20px rgba(59, 130, 246, 0.2);
    user-select: none;
    touch-action: manipulation;
}
.primary-btn:hover { transform: translateY(-2px) scale(1.02); box-shadow: 0 12px 25px rgba(59, 130, 246, 0.3); }
.primary-btn:active { transform: translateY(1px) scale(0.98); }

.options-grid { display: flex; flex-direction: column; gap: 14px; width: 100%; }
.option-btn {
    display: flex; align-items: center; background: rgba(255,255,255, 0.4);
    border: 2px solid transparent; padding: 14px 20px; border-radius: 16px;
    cursor: pointer; text-align: left; font-size: 1.05rem; font-weight: 500; line-height: 1.5;
    color: var(--text-primary); font-family: var(--font-vn);
    transition: all 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275); position: relative; overflow: hidden; min-height: 64px;
    box-shadow: 0 4px 6px rgba(0,0,0,0.02);
    user-select: none;
    touch-action: manipulation;
}
[data-theme="dark"] .option-btn { background: rgba(255,255,255, 0.03); border: 2px solid rgba(255,255,255,0.02); box-shadow: none; }

.option-btn .ripple {
    position: absolute; border-radius: 50%; transform: scale(0);
    animation: ripple-effect 0.4s linear; background-color: rgba(0, 0, 0, 0.05); pointer-events: none;
}
[data-theme="dark"] .option-btn .ripple { background-color: rgba(255, 255, 255, 0.05); }
@keyframes ripple-effect { to { transform: scale(4); opacity: 0; } }

.option-btn:hover:not(:disabled) {
    transform: translateY(-2px) scale(1.01);
    background: white;
    border-color: rgba(59, 130, 246, 0.3);
    box-shadow: 0 8px 25px rgba(59, 130, 246, 0.1);
}
[data-theme="dark"] .option-btn:hover:not(:disabled) { background: rgba(255,255,255, 0.08); border-color: rgba(59, 130, 246, 0.4); }

.option-circle {
    width: 36px; height: 36px; border-radius: 10px; background: rgba(0,0,0,0.05); border: none;
    margin-right: 16px; display: flex; align-items: center; justify-content: center;
    flex-shrink: 0; transition: all 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275); font-size: 14px; font-weight: 700; color: var(--text-secondary);
}
[data-theme="dark"] .option-circle { background: rgba(255,255,255,0.1); }

.option-btn:hover:not(:disabled) .option-circle {
    background: rgba(59, 130, 246, 0.15);
    color: var(--primary);
    transform: scale(1.1);
}

.option-btn.selected { transform: scale(1.02); }
.option-btn.selected .option-circle { background: var(--primary); color: white; }
.option-btn.correct { border-color: var(--success); background: rgba(34, 197, 94, 0.05); transform: translateY(-4px) scale(1.02); box-shadow: 0 10px 25px rgba(34, 197, 94, 0.2); }
[data-theme="dark"] .option-btn.correct { background: rgba(34, 197, 94, 0.1); }
.option-btn.correct .option-circle { background: var(--success); color: white; font-size: 0; transform: scale(1.1); }
.option-btn.correct .option-circle::after { content: ''; width: 12px; height: 6px; border-left: 2.5px solid white; border-bottom: 2.5px solid white; transform: rotate(-45deg) translateY(-1.5px); display: block; animation: pop-in 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275); }
.option-btn.wrong { border-color: var(--error); background: rgba(239, 68, 68, 0.05); animation: shake-short 0.35s ease-in-out; }
[data-theme="dark"] .option-btn.wrong { background: rgba(239, 68, 68, 0.1); }
.option-btn.wrong .option-circle { background: var(--error); color: white; }

@keyframes pop-in { 0% { transform: scale(0); } 70% { transform: scale(1.2); } 100% { transform: scale(1); } }
@keyframes shake-short { 0%, 100% { transform: translateX(0); } 25% { transform: translateX(-8px); } 50% { transform: translateX(8px); } 75% { transform: translateX(-4px); } }

.question-container { width: 100%; position: relative; }
.slide-out-left { animation: slideOutLeft 0.3s forwards ease-in; }
.slide-in-right { animation: slideInRight 0.3s forwards ease-out; }
@keyframes slideOutLeft { to { opacity: 0; transform: translateX(-20px); } }
@keyframes slideInRight { from { opacity: 0; transform: translateX(20px); } to { opacity: 1; transform: translateX(0); } }

.feedback-container { margin-top: 24px; text-align: center; }
.feedback-text { font-size: 1.1rem; font-weight: 600; margin-bottom: 16px; }
.feedback-correct { color: var(--success); }
.feedback-wrong { color: var(--error); }

.stats-board { display: flex; flex-direction: column; gap: 12px; margin-top: 24px; background: rgba(0,0,0,0.02); padding: 24px; border-radius: 20px; border: 1px solid var(--card-border); }
[data-theme="dark"] .stats-board { background: rgba(255,255,255,0.02); }
.stat-row { display: flex; justify-content: space-between; align-items: center; font-size: 1.1rem; border-bottom: 1px solid rgba(0,0,0,0.05); padding-bottom: 12px; }
[data-theme="dark"] .stat-row { border-bottom: 1px solid rgba(255,255,255,0.05); }
.stat-row:last-child { border-bottom: none; padding-bottom: 0; }
.stat-label { font-weight: 500; color: var(--text-secondary); }
.stat-value { font-weight: 700; color: var(--text-primary); font-family: var(--font-en); }

.chart-bar { height: 24px; border-radius: 12px; transition: width 1s cubic-bezier(0.175, 0.885, 0.32, 1.275); }
.correct-bar { background: var(--success); width: 0%; box-shadow: 0 4px 10px rgba(34, 197, 94, 0.2); }
.wrong-bar { background: var(--error); width: 0%; box-shadow: 0 4px 10px rgba(239, 68, 68, 0.2); }

/* Toggle Switches */
.toggle-switch { position: relative; display: inline-block; width: 44px; height: 24px; margin-right: 12px; flex-shrink: 0; }
.toggle-switch input { opacity: 0; width: 0; height: 0; }
.toggle-slider { position: absolute; cursor: pointer; top: 0; left: 0; right: 0; bottom: 0; background-color: rgba(0,0,0,0.15); transition: .3s; border-radius: 24px; user-select: none; touch-action: manipulation; }
[data-theme="dark"] .toggle-slider { background-color: rgba(255,255,255,0.15); }
.toggle-slider:before { position: absolute; content: ""; height: 18px; width: 18px; left: 3px; bottom: 3px; background-color: white; transition: .3s cubic-bezier(0.175, 0.885, 0.32, 1.275); border-radius: 50%; box-shadow: 0 2px 5px rgba(0,0,0,0.2); }
input:checked + .toggle-slider { background-color: var(--primary); }
input:checked + .toggle-slider:before { transform: translateX(20px); }

.bottom-nav {
    display: none; position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%);
    background: var(--card-bg); backdrop-filter: blur(24px); -webkit-backdrop-filter: blur(24px);
    border: 1px solid var(--card-border); border-radius: 100px; padding: 12px 24px;
    width: 90%; max-width: 400px; justify-content: space-between; box-shadow: 0 10px 25px rgba(0,0,0,0.05); z-index: 10;
}
.bottom-nav button { background: none; border: none; font-size: 0.95rem; font-weight: 600; color: var(--text-secondary); cursor: pointer; transition: 0.2s; font-family: var(--font-vn); user-select: none; touch-action: manipulation; }
.bottom-nav button.active { color: var(--primary); transform: translateY(-2px); }

@media (max-width: 768px) {
    .top-nav .nav-links { display: none !important; }
    .bottom-nav { display: flex; }
    .app-container { width: 95%; padding: 32px 20px; border-radius: 24px; min-height: 75vh; margin-bottom: 80px; }
}

/* Modal Styling */
.modal { position: fixed; top: 0; left: 0; width: 100vw; height: 100vh; background: rgba(0,0,0,0.4); backdrop-filter: blur(8px); -webkit-backdrop-filter: blur(8px); z-index: 1000; display: flex; justify-content: center; align-items: center; opacity: 1; transition: opacity 0.3s; }
.modal.hidden { opacity: 0; pointer-events: none; display: flex !important; }
.modal-content { background: var(--card-bg); border: 1px solid var(--card-border); border-radius: 24px; padding: 32px; width: 90%; max-width: 500px; box-shadow: 0 20px 40px rgba(0,0,0,0.1); position: relative; max-height: 85vh; overflow-y: auto; transform: translateY(0); transition: transform 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275); }
.modal.hidden .modal-content { transform: translateY(20px); }
.close-btn { position: absolute; top: 20px; right: 24px; background: none; border: none; font-size: 2rem; cursor: pointer; color: var(--text-secondary); transition: 0.2s; line-height: 1; }
.close-btn:hover { color: var(--text-primary); transform: scale(1.1); }

.modal-tabs { display: flex; gap: 8px; margin-bottom: 24px; border-bottom: 2px solid var(--card-border); padding-bottom: 8px; }
.tab-btn { background: none; border: none; padding: 8px 16px; font-size: 1.05rem; font-weight: 600; color: var(--text-secondary); cursor: pointer; transition: 0.2s; border-radius: 12px; font-family: var(--font-vn); }
.tab-btn:hover { background: rgba(0,0,0,0.05); }
[data-theme="dark"] .tab-btn:hover { background: rgba(255,255,255,0.05); }
.tab-btn.active { color: var(--primary); background: rgba(59,130,246,0.1); }

.tab-content { display: none; }
.tab-content.active { display: block; animation: fade-in 0.3s; }

/* Leaderboard */
.leaderboard-list { display: flex; flex-direction: column; gap: 12px; }
.leaderboard-item { display: flex; justify-content: space-between; align-items: center; padding: 12px 16px; background: rgba(0,0,0,0.02); border-radius: 12px; border: 1px solid var(--card-border); }
[data-theme="dark"] .leaderboard-item { background: rgba(255,255,255,0.02); }
.lb-rank { font-weight: 700; width: 30px; color: var(--text-secondary); }
.lb-score { font-weight: 700; color: var(--primary); font-size: 1.1rem; }
.lb-time { font-size: 0.9rem; color: var(--text-secondary); }

/* Stats */
.stats-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.stat-card { background: rgba(0,0,0,0.02); border: 1px solid var(--card-border); padding: 16px; border-radius: 16px; text-align: center; }
[data-theme="dark"] .stat-card { background: rgba(255,255,255,0.02); }
.stat-card-label { font-size: 0.9rem; color: var(--text-secondary); margin-bottom: 8px; font-weight: 500; }
.stat-card-value { font-size: 1.5rem; font-weight: 700; color: var(--primary); }

.hidden { display: none !important; }
.keyboard-hint { font-size: 0.85rem; color: var(--text-secondary); text-align: center; margin-bottom: 24px; opacity: 0.7; }
.wrong-answers-container { margin-top: 30px; text-align: left; width: 100%; background: rgba(0,0,0,0.02); padding: 24px; border-radius: 20px; border: 1px solid var(--card-border); }
[data-theme="dark"] .wrong-answers-container { background: rgba(255,255,255,0.02); }
.wrong-item { margin-bottom: 12px; padding-bottom: 12px; border-bottom: 1px solid var(--card-border); font-size: 0.95rem; }
.wrong-q { font-weight: 600; margin-bottom: 6px; }
.wrong-a { color: var(--success); font-weight: 600; }