:root {
    --primary-color: #2196F3;
    --success-color: #4CAF50;
    --warning-color: #FFC107;
    --danger-color: #F44336;
    --purple-color: #9C27B0;
    --dark-color: #333;
    --light-color: #f5f5f5;
    --white-color: #ffffff;
    --shadow: 0 2px 10px rgba(0,0,0,0.1);
    --border-radius: 12px;
    --transition: all 0.3s ease;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background: linear-gradient(135deg, var(--light-color) 0%, #e8e8e8 100%);
    min-height: 100vh;
    color: var(--dark-color);
    padding-bottom: 80px;
}

.app-header {
    background: linear-gradient(135deg, var(--primary-color), #1976D2);
    color: white;
    padding: 1rem;
    text-align: center;
    box-shadow: var(--shadow);
    position: sticky;
    top: 0;
    z-index: 100;
}

.app-header h1 {
    font-size: 1.5rem;
    margin-bottom: 0.5rem;
}

.header-stats {
    display: flex;
    justify-content: center;
    gap: 2rem;
    font-size: 0.9rem;
}

.app-main {
    padding: 1rem;
    max-width: 1200px;
    margin: 0 auto;
}

.app-section {
    display: none;
    animation: fadeIn 0.3s ease;
}

.app-section.active {
    display: block;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(20px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Welcome Card */
.welcome-card {
    background: var(--white-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    text-align: center;
    margin-bottom: 2rem;
    background-image: 
        radial-gradient(circle at 25px 25px, rgba(255,255,255,0.2) 2%, transparent 0%),
        radial-gradient(circle at 75px 75px, rgba(255,255,255,0.1) 2%, transparent 0%);
    background-size: 100px 100px;
}

.welcome-card h2 {
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-size: 1.8rem;
}

/* Game Modes */
.game-modes {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1rem;
    margin-bottom: 2rem;
}

.mode-card {
    background: var(--white-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    text-align: center;
    cursor: pointer;
    transition: var(--transition);
    border: 2px solid transparent;
}

.mode-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 5px 20px rgba(0,0,0,0.15);
    border-color: var(--primary-color);
}

.mode-card i {
    font-size: 3rem;
    color: var(--primary-color);
    margin-bottom: 1rem;
}

.mode-card h3 {
    margin-bottom: 0.5rem;
    color: var(--dark-color);
}

.mode-card p {
    color: #666;
    font-size: 0.9rem;
}

/* Quick Stats */
.quick-stats {
    display: flex;
    justify-content: space-around;
    background: var(--white-color);
    padding: 1.5rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
}

.stat-item {
    text-align: center;
}

.stat-number {
    display: block;
    font-size: 2rem;
    font-weight: bold;
    color: var(--primary-color);
}

.stat-label {
    font-size: 0.8rem;
    color: #666;
    text-transform: uppercase;
}

/* Game Setup */
.setup-header, .questions-header, .multiplayer-header, .learning-header, .profile-header, .leaderboard-header, .faq-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 2rem;
}

.back-btn {
    background: var(--light-color);
    border: none;
    padding: 0.75rem 1rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
    color: var(--dark-color);
    font-size: 0.9rem;
}

.back-btn:hover {
    background: #ddd;
}

.game-config {
    background: var(--white-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
}

.config-group {
    margin-bottom: 1.5rem;
}

.config-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: var(--dark-color);
}

.config-group select,
.config-group input {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid #ddd;
    border-radius: var(--border-radius);
    font-size: 1rem;
    transition: var(--transition);
}

.config-group select:focus,
.config-group input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.1);
}

.start-game-btn {
    width: 100%;
    background: linear-gradient(135deg, var(--success-color), #45a049);
    color: white;
    border: none;
    padding: 1rem;
    border-radius: var(--border-radius);
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
}

.start-game-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(76, 175, 80, 0.3);
}

/* Game Play */
.game-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: var(--white-color);
    padding: 1rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    margin-bottom: 1.5rem;
    flex-wrap: wrap;
    gap: 1rem;
}

.game-progress, .game-score, .game-timer {
    font-weight: 600;
    color: var(--dark-color);
}

.game-timer {
    color: var(--danger-color);
    font-size: 1.1rem;
}

.question-card {
    background: var(--white-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    margin-bottom: 2rem;
    text-align: center;
}

.question-category {
    display: inline-block;
    background: var(--primary-color);
    color: white;
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    font-size: 0.8rem;
    margin-bottom: 0.5rem;
}

.question-difficulty {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    font-size: 0.8rem;
    margin-bottom: 1rem;
    margin-left: 0.5rem;
}

.question-difficulty.easy { background: var(--success-color); color: white; }
.question-difficulty.medium { background: var(--warning-color); color: white; }
.question-difficulty.hard { background: var(--danger-color); color: white; }

#question-text {
    font-size: 1.3rem;
    line-height: 1.5;
    color: var(--dark-color);
}

.answers-container {
    display: grid;
    gap: 1rem;
    margin-bottom: 2rem;
}

.answer-btn {
    background: var(--white-color);
    border: 2px solid #ddd;
    padding: 1rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
    text-align: left;
    font-size: 1rem;
    color: var(--dark-color);
}

.answer-btn:hover {
    border-color: var(--primary-color);
    background: rgba(33, 150, 243, 0.05);
}

.answer-btn.correct {
    background: var(--success-color);
    color: white;
    border-color: var(--success-color);
}

.answer-btn.incorrect {
    background: var(--danger-color);
    color: white;
    border-color: var(--danger-color);
}

.answer-btn.selected {
    border-color: var(--primary-color);
    background: var(--primary-color);
    color: white;
}

.game-actions {
    text-align: center;
}

.skip-btn {
    background: var(--warning-color);
    color: white;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
}

.skip-btn:hover {
    background: #e6a100;
}

/* Game Results */
.results-header {
    text-align: center;
    margin-bottom: 2rem;
}

.results-summary {
    background: var(--white-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    text-align: center;
    margin-bottom: 2rem;
}

.final-score {
    margin-bottom: 2rem;
}

.score-label {
    display: block;
    font-size: 1rem;
    color: #666;
    margin-bottom: 0.5rem;
}

.score-value {
    display: block;
    font-size: 3rem;
    font-weight: bold;
    color: var(--primary-color);
}

.results-stats {
    display: flex;
    justify-content: space-around;
    gap: 1rem;
}

.result-stat {
    text-align: center;
}

.result-stat .stat-value {
    display: block;
    font-size: 1.8rem;
    font-weight: bold;
    color: var(--success-color);
}

.result-stat .stat-label {
    font-size: 0.9rem;
    color: #666;
}

.results-actions {
    display: flex;
    gap: 1rem;
    justify-content: center;
}

.play-again-btn, .home-btn {
    padding: 1rem 2rem;
    border: none;
    border-radius: var(--border-radius);
    font-size: 1rem;
    cursor: pointer;
    transition: var(--transition);
}

.play-again-btn {
    background: var(--success-color);
    color: white;
}

.home-btn {
    background: var(--light-color);
    color: var(--dark-color);
}

.play-again-btn:hover, .home-btn:hover {
    transform: translateY(-2px);
}

/* Multiplayer */
.multiplayer-content {
    background: var(--white-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
}

.player-setup {
    margin-bottom: 2rem;
}

.input-group {
    margin-bottom: 1.5rem;
}

.input-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
}

.input-group input {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid #ddd;
    border-radius: var(--border-radius);
    font-size: 1rem;
}

.room-options {
    display: flex;
    gap: 1rem;
}

.room-btn {
    flex: 1;
    padding: 1rem;
    border: none;
    border-radius: var(--border-radius);
    background: var(--primary-color);
    color: white;
    cursor: pointer;
    transition: var(--transition);
}

.room-btn:hover {
    background: #1976D2;
}

.room-input {
    display: flex;
    gap: 1rem;
    align-items: end;
    margin-bottom: 2rem;
}

.room-input label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
}

.room-input input {
    flex: 1;
    padding: 0.75rem;
    border: 2px solid #ddd;
    border-radius: var(--border-radius);
}

.room-input button {
    padding: 0.75rem 1.5rem;
    background: var(--success-color);
    color: white;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
}

.room-info {
    text-align: center;
}

.room-info h3 {
    margin-bottom: 1rem;
    color: var(--primary-color);
}

.players-list {
    margin-bottom: 2rem;
}

.players-list ul {
    list-style: none;
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    justify-content: center;
}

.players-list li {
    background: var(--light-color);
    padding: 0.5rem 1rem;
    border-radius: 20px;
    font-size: 0.9rem;
}

.start-mp-btn {
    background: var(--success-color);
    color: white;
    border: none;
    padding: 1rem 2rem;
    border-radius: var(--border-radius);
    font-size: 1.1rem;
    cursor: pointer;
    transition: var(--transition);
}

/* Learning Mode */
.learning-content {
    background: var(--white-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
}

.learning-setup h3 {
    text-align: center;
    margin-bottom: 2rem;
    color: var(--dark-color);
}

.topics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1rem;
}

.topic-card {
    background: var(--light-color);
    padding: 1.5rem;
    border-radius: var(--border-radius);
    text-align: center;
    cursor: pointer;
    transition: var(--transition);
    border: 2px solid transparent;
}

.topic-card:hover {
    border-color: var(--primary-color);
    background: rgba(33, 150, 243, 0.05);
}

.topic-card i {
    font-size: 2rem;
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

.learning-question {
    text-align: center;
}

.question-info {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
}

.topic-name {
    background: var(--purple-color);
    color: white;
    padding: 0.5rem 1rem;
    border-radius: 20px;
    font-size: 0.9rem;
}

.question-number {
    color: #666;
    font-weight: 600;
}

.learning-question-text {
    font-size: 1.3rem;
    margin-bottom: 2rem;
    line-height: 1.5;
}

.learning-answers {
    display: grid;
    gap: 1rem;
    margin-bottom: 2rem;
}

.explanation {
    background: var(--light-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    text-align: left;
    margin-top: 2rem;
}

.explanation h4 {
    margin-bottom: 1rem;
    color: var(--primary-color);
}

.next-btn {
    background: var(--primary-color);
    color: white;
    border: none;
    padding: 1rem 2rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    margin-top: 1rem;
    transition: var(--transition);
}

.next-btn:hover {
    background: #1976D2;
}

/* Questions Manager */
.questions-filters {
    display: flex;
    gap: 1rem;
    margin-bottom: 2rem;
}

.questions-filters select {
    flex: 1;
    padding: 0.75rem;
    border: 2px solid #ddd;
    border-radius: var(--border-radius);
}

.add-btn {
    background: var(--success-color);
    color: white;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
}

.add-btn:hover {
    background: #45a049;
}

.questions-list {
    display: grid;
    gap: 1rem;
}

.question-item {
    background: var(--white-color);
    padding: 1.5rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    border-left: 4px solid var(--primary-color);
}

.question-item-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: 1rem;
}

.question-meta {
    display: flex;
    gap: 0.5rem;
    flex-wrap: wrap;
}

.question-meta span {
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    font-size: 0.8rem;
    color: white;
}

.category-tag {
    background: var(--primary-color);
}

.difficulty-tag.easy { background: var(--success-color); }
.difficulty-tag.medium { background: var(--warning-color); }
.difficulty-tag.hard { background: var(--danger-color); }

.question-actions {
    display: flex;
    gap: 0.5rem;
}

.edit-btn, .delete-btn {
    padding: 0.5rem;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 0.9rem;
}

.edit-btn {
    background: var(--warning-color);
    color: white;
}

.delete-btn {
    background: var(--danger-color);
    color: white;
}

.question-text {
    font-weight: 600;
    margin-bottom: 1rem;
    color: var(--dark-color);
}

.question-answers {
    display: grid;
    gap: 0.5rem;
}

.answer-item {
    padding: 0.5rem;
    border-radius: var(--border-radius);
    font-size: 0.9rem;
}

.answer-item.correct {
    background: rgba(76, 175, 80, 0.1);
    border-left: 3px solid var(--success-color);
}

.answer-item.incorrect {
    background: var(--light-color);
}

/* Modal */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    padding: 1rem;
}

.modal-content {
    background: var(--white-color);
    border-radius: var(--border-radius);
    width: 100%;
    max-width: 600px;
    max-height: 90vh;
    overflow-y: auto;
}

.modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1.5rem;
    border-bottom: 1px solid #eee;
}

.close-modal {
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: #666;
}

.modal form {
    padding: 2rem;
}

.form-group {
    margin-bottom: 1.5rem;
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
}

.form-group input,
.form-group select,
.form-group textarea {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid #ddd;
    border-radius: var(--border-radius);
    font-size: 1rem;
}

.form-group textarea {
    resize: vertical;
    min-height: 100px;
}

.answers-input {
    margin-bottom: 1.5rem;
}

.answers-input h4 {
    margin-bottom: 1rem;
    color: var(--dark-color);
}

.answer-option {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin-bottom: 1rem;
}

.answer-option input[type="text"] {
    flex: 1;
}

.answer-option label {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    white-space: nowrap;
    margin-bottom: 0;
}

.form-actions {
    display: flex;
    gap: 1rem;
    justify-content: flex-end;
}

.save-btn {
    background: var(--success-color);
    color: white;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius);
    cursor: pointer;
}

.cancel-btn {
    background: var(--light-color);
    color: var(--dark-color);
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius);
    cursor: pointer;
}

/* Profile */
.profile-content {
    background: var(--white-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
}

.profile-stats {
    display: flex;
    align-items: center;
    gap: 2rem;
    margin-bottom: 3rem;
    padding-bottom: 2rem;
    border-bottom: 1px solid #eee;
}

.profile-avatar i {
    font-size: 4rem;
    color: var(--primary-color);
}

.profile-info h3 {
    font-size: 1.5rem;
    margin-bottom: 0.5rem;
    color: var(--dark-color);
}

.profile-info p {
    color: #666;
    margin-bottom: 1rem;
}

.level-progress {
    width: 200px;
}

.progress-bar {
    height: 8px;
    background: var(--light-color);
    border-radius: 4px;
    overflow: hidden;
    margin-bottom: 0.5rem;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary-color), var(--purple-color));
    width: 0%;
    transition: width 0.3s ease;
}

#level-progress-text {
    font-size: 0.8rem;
    color: #666;
}

.achievements {
    margin-bottom: 3rem;
}

.achievements h3 {
    margin-bottom: 1.5rem;
    color: var(--dark-color);
}

.achievements-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 1rem;
}

.achievement-item {
    text-align: center;
    padding: 1rem;
    border-radius: var(--border-radius);
    background: var(--light-color);
    transition: var(--transition);
}

.achievement-item.unlocked {
    background: linear-gradient(135deg, var(--warning-color), #e6a100);
    color: white;
}

.achievement-item i {
    font-size: 2rem;
    margin-bottom: 0.5rem;
    display: block;
}

.achievement-item h4 {
    font-size: 0.9rem;
    margin-bottom: 0.25rem;
}

.achievement-item p {
    font-size: 0.8rem;
    opacity: 0.8;
}

.profile-settings h3 {
    margin-bottom: 1.5rem;
    color: var(--dark-color);
}

.settings-form {
    display: grid;
    gap: 1.5rem;
}

.setting-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.setting-item label {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    cursor: pointer;
}

.setting-item input[type="text"] {
    flex: 1;
    padding: 0.75rem;
    border: 2px solid #ddd;
    border-radius: var(--border-radius);
}

.setting-item input[type="checkbox"] {
    width: 20px;
    height: 20px;
}

.save-settings-btn {
    background: var(--primary-color);
    color: white;
    border: none;
    padding: 1rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 1rem;
    transition: var(--transition);
}

.save-settings-btn:hover {
    background: #1976D2;
}

/* Leaderboard */
.leaderboard-tabs {
    display: flex;
    gap: 0.5rem;
}

.tab-btn {
    padding: 0.75rem 1.5rem;
    border: none;
    background: var(--light-color);
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
}

.tab-btn.active {
    background: var(--primary-color);
    color: white;
}

.leaderboard-content {
    background: var(--white-color);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    overflow: hidden;
}

.leaderboard-list {
    display: grid;
    gap: 0;
}

.leaderboard-item {
    display: flex;
    align-items: center;
    padding: 1rem;
    border-bottom: 1px solid #eee;
    transition: var(--transition);
}

.leaderboard-item:hover {
    background: var(--light-color);
}

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

.leaderboard-rank {
    font-size: 1.5rem;
    font-weight: bold;
    margin-right: 1rem;
    width: 3rem;
    text-align: center;
}

.leaderboard-rank.first { color: #FFD700; }
.leaderboard-rank.second { color: #C0C0C0; }
.leaderboard-rank.third { color: #CD7F32; }

.leaderboard-avatar {
    margin-right: 1rem;
}

.leaderboard-avatar i {
    font-size: 2rem;
    color: var(--primary-color);
}

.leaderboard-info {
    flex: 1;
}

.leaderboard-name {
    font-weight: 600;
    margin-bottom: 0.25rem;
}

.leaderboard-stats {
    font-size: 0.9rem;
    color: #666;
}

.leaderboard-score {
    font-size: 1.2rem;
    font-weight: bold;
    color: var(--success-color);
}

/* FAQ */
.faq-container {
    background: var(--white-color);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    overflow: hidden;
}

.faq-item {
    border-bottom: 1px solid #eee;
}

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

.faq-question {
    width: 100%;
    padding: 1.5rem;
    border: none;
    background: none;
    text-align: left;
    cursor: pointer;
    font-size: 1rem;
    font-weight: 600;
    color: var(--dark-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: var(--transition);
}

.faq-question:hover {
    background: var(--light-color);
}

.faq-question[aria-expanded="true"] {
    background: var(--light-color);
}

.faq-icon {
    font-size: 1.5rem;
    color: var(--primary-color);
    transition: transform 0.3s ease;
}

.faq-question[aria-expanded="true"] .faq-icon {
    transform: rotate(45deg);
}

.faq-answer {
    padding: 0 1.5rem 1.5rem;
    color: #666;
    line-height: 1.6;
    animation: slideDown 0.3s ease;
}

@keyframes slideDown {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Bottom Navigation */
.bottom-nav {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    background: var(--white-color);
    display: flex;
    box-shadow: 0 -2px 10px rgba(0,0,0,0.1);
    z-index: 100;
}

.nav-item {
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 0.75rem 0.5rem;
    text-decoration: none;
    color: #666;
    transition: var(--transition);
    border-top: 3px solid transparent;
}

.nav-item.active {
    color: var(--primary-color);
    border-top-color: var(--primary-color);
}

.nav-item i {
    font-size: 1.2rem;
    margin-bottom: 0.25rem;
}

.nav-item span {
    font-size: 0.7rem;
    font-weight: 600;
}

/* Footer */
footer {
    text-align: center;
    padding: 2rem 1rem;
    color: #666;
    font-size: 0.9rem;
    background: var(--white-color);
    margin-top: 2rem;
    border-top: 1px solid #eee;
}

/* Loading Screen */
.loading-screen {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: var(--white-color);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 9999;
}

.loading-content {
    text-align: center;
}

.loading-spinner {
    width: 50px;
    height: 50px;
    border: 4px solid var(--light-color);
    border-top: 4px solid var(--primary-color);
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin: 0 auto 1rem;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Utility Classes */
.hidden {
    display: none !important;
}

.text-center {
    text-align: center;
}

.mb-1 { margin-bottom: 1rem; }
.mb-2 { margin-bottom: 2rem; }
.mt-1 { margin-top: 1rem; }
.mt-2 { margin-top: 2rem; }

/* Responsive Design */
@media (max-width: 768px) {
    .app-main {
        padding: 0.5rem;
    }
    
    .welcome-card {
        padding: 1.5rem;
    }
    
    .welcome-card h2 {
        font-size: 1.5rem;
    }
    
    .game-modes {
        grid-template-columns: 1fr;
    }
    
    .mode-card {
        padding: 1.5rem;
    }
    
    .quick-stats {
        padding: 1rem;
    }
    
    .header-stats {
        gap: 1rem;
        font-size: 0.8rem;
    }
    
    .game-header {
        flex-direction: column;
        gap: 0.5rem;
    }
    
    .question-card {
        padding: 1.5rem;
    }
    
    #question-text {
        font-size: 1.1rem;
    }
    
    .results-stats {
        flex-direction: column;
        gap: 1rem;
    }
    
    .results-actions {
        flex-direction: column;
    }
    
    .room-options {
        flex-direction: column;
    }
    
    .room-input {
        flex-direction: column;
        align-items: stretch;
    }
    
    .questions-filters {
        flex-direction: column;
    }
    
    .setup-header, .questions-header, .multiplayer-header, .learning-header, .profile-header, .leaderboard-header, .faq-header {
        flex-direction: column;
        gap: 1rem;
        text-align: center;
    }
    
    .profile-stats {
        flex-direction: column;
        text-align: center;
        gap: 1rem;
    }
    
    .achievements-grid {
        grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    }
    
    .leaderboard-tabs {
        flex-wrap: wrap;
    }
    
    .modal {
        padding: 0.5rem;
    }
    
    .modal-content {
        max-height: 95vh;
    }
    
    .form-actions {
        flex-direction: column;
    }
}

@media (max-width: 480px) {
    .nav-item span {
        font-size: 0.6rem;
    }
    
    .nav-item i {
        font-size: 1rem;
    }
    
    .stat-number {
        font-size: 1.5rem;
    }
    
    .question-info {
        flex-direction: column;
        gap: 1rem;
    }
    
    .answer-option {
        flex-direction: column;
        align-items: stretch;
        gap: 0.5rem;
    }
}