/* CSS Variables for theming */
:root {
    --bg-primary: #f5f7fa;
    --bg-secondary: #ffffff;
    --bg-card: #ffffff;
    --text-primary: #1a202c;
    --text-secondary: #4a5568;
    --text-muted: #718096;
    --border-color: #e2e8f0;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.15);
    --primary: #4299e1;
    --primary-dark: #2b6cb0;
    --success: #48bb78;
    --warning: #ed8936;
    --danger: #f56565;
    --masculine: #4299e1;
    --feminine: #d53f8c;
    --transition: all 0.3s ease;
}

[data-theme="dark"] {
    --bg-primary: #1a202c;
    --bg-secondary: #2d3748;
    --bg-card: #2d3748;
    --text-primary: #f7fafc;
    --text-secondary: #e2e8f0;
    --text-muted: #a0aec0;
    --border-color: #4a5568;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.4);
}

/* Base styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
}

body {
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    transition: var(--transition);
}

.app-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
.header {
    background: var(--bg-secondary);
    padding: 20px;
    border-radius: 12px;
    margin-bottom: 20px;
    box-shadow: var(--shadow);
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 15px;
}

.header h1 {
    font-size: 1.8rem;
    color: var(--text-primary);
}

.header-controls {
    display: flex;
    gap: 10px;
}

.icon-btn {
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    padding: 8px 16px;
    border-radius: 8px;
    font-size: 1.2rem;
    cursor: pointer;
    transition: var(--transition);
}

.icon-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}

.streak-info {
    display: flex;
    gap: 20px;
    color: var(--text-secondary);
    font-size: 0.95rem;
}

/* Main Content */
.main-content {
    flex: 1;
}

.screen {
    display: none;
    animation: fadeIn 0.3s ease;
}

.screen.active {
    display: block;
}

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

/* Welcome Screen */
.welcome-content {
    background: var(--bg-secondary);
    padding: 40px;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.welcome-content h2 {
    font-size: 2rem;
    margin-bottom: 10px;
    text-align: center;
}

.subtitle {
    text-align: center;
    color: var(--text-secondary);
    margin-bottom: 40px;
    font-size: 1.1rem;
}

/* Level Selector */
.level-selector {
    margin-bottom: 40px;
}

.level-selector h3 {
    margin-bottom: 20px;
    color: var(--text-primary);
}

.level-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 20px;
}

.level-card {
    background: var(--bg-card);
    border: 2px solid var(--border-color);
    border-radius: 12px;
    padding: 24px;
    cursor: pointer;
    transition: var(--transition);
    position: relative;
}

.level-card:hover:not(.disabled) {
    border-color: var(--primary);
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
}

.level-card.selected {
    border-color: var(--primary);
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    color: white;
}

.level-card.disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.level-badge {
    display: inline-block;
    background: var(--primary);
    color: white;
    padding: 6px 12px;
    border-radius: 20px;
    font-weight: bold;
    font-size: 0.85rem;
    margin-bottom: 12px;
}

.level-card h4 {
    margin-bottom: 8px;
    font-size: 1.3rem;
}

.level-card > p {
    color: var(--text-secondary);
    margin-bottom: 8px;
}

.level-desc {
    font-size: 0.9rem;
    margin-bottom: 16px;
}

.level-progress {
    margin-top: 16px;
}

.progress-bar {
    background: var(--bg-primary);
    height: 8px;
    border-radius: 4px;
    overflow: hidden;
    margin-bottom: 8px;
}

.progress-fill {
    background: linear-gradient(90deg, var(--success) 0%, var(--primary) 100%);
    height: 100%;
    transition: width 0.5s ease;
}

.progress-text {
    font-size: 0.85rem;
    color: var(--text-muted);
}

/* Mode Selector */
.mode-selector h3 {
    margin-bottom: 20px;
}

.mode-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 15px;
}

.mode-btn {
    background: var(--bg-card);
    border: 2px solid var(--border-color);
    border-radius: 12px;
    padding: 20px;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    text-align: left;
}

.mode-btn:hover {
    border-color: var(--primary);
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}

.mode-btn.primary {
    border-color: var(--primary);
    background: linear-gradient(135deg, rgba(66, 153, 225, 0.1) 0%, rgba(66, 153, 225, 0.05) 100%);
}

.mode-icon {
    font-size: 2rem;
    margin-bottom: 10px;
}

.mode-title {
    font-weight: bold;
    font-size: 1.2rem;
    margin-bottom: 5px;
    color: var(--text-primary);
}

.mode-desc {
    color: var(--text-secondary);
    font-size: 0.9rem;
    margin-bottom: 8px;
}

.cards-due {
    color: var(--primary);
    font-weight: bold;
    margin-top: 8px;
}

/* Flashcard Screen */
.session-header {
    background: var(--bg-secondary);
    padding: 15px 20px;
    border-radius: 12px;
    margin-bottom: 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: var(--shadow);
}

.session-info {
    display: flex;
    gap: 20px;
    font-weight: bold;
    color: var(--text-secondary);
}

.session-progress-bar {
    flex: 1;
    max-width: 300px;
    background: var(--bg-primary);
    height: 8px;
    border-radius: 4px;
    overflow: hidden;
    margin-left: 20px;
}

/* Flashcard */
.flashcard-container {
    perspective: 1000px;
    margin-bottom: 30px;
    min-height: 400px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.flashcard {
    width: 100%;
    max-width: 700px;
    height: 450px;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.1s cubic-bezier(0.4, 0.0, 0.2, 1);
    cursor: pointer;
}

.flashcard.flipped {
    transform: rotateY(180deg);
}

.card-face {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    background: var(--bg-secondary);
    border-radius: 16px;
    padding: 40px;
    box-shadow: var(--shadow-lg);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
}

.card-front {
    opacity: 1;
}

.card-back {
    transform: rotateY(180deg);
    opacity: 0;
}

/* When card is flipped, show back and hide front */
.flashcard.flipped .card-front {
    opacity: 0;
}

.flashcard.flipped .card-back {
    opacity: 1;
}

.card-label {
    position: absolute;
    top: 20px;
    left: 20px;
    color: var(--text-muted);
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 1px;
}

.card-content {
    font-size: 2.5rem;
    font-weight: bold;
    color: var(--text-primary);
    margin: 20px 0;
}

.flip-hint {
    position: absolute;
    bottom: 20px;
    color: var(--text-muted);
    font-size: 0.9rem;
}

.card-meta {
    display: flex;
    gap: 20px;
    margin-top: 20px;
    align-items: center;
}

.card-gender {
    padding: 6px 12px;
    border-radius: 20px;
    font-size: 0.85rem;
    font-weight: bold;
}

.card-gender.masculine {
    background: rgba(66, 153, 225, 0.2);
    color: var(--masculine);
}

.card-gender.feminine {
    background: rgba(213, 63, 140, 0.2);
    color: var(--feminine);
}

.card-pronunciation {
    color: var(--text-secondary);
    font-style: italic;
}

.card-context {
    margin-top: 24px;
    padding: 16px;
    background: var(--bg-primary);
    border-radius: 8px;
    color: var(--text-secondary);
    font-size: 1.1rem;
    max-width: 90%;
}

.card-notes {
    margin-top: 16px;
    color: var(--text-muted);
    font-size: 0.9rem;
}

/* Controls */
.controls {
    margin-bottom: 20px;
}

.navigation-controls {
    display: flex;
    justify-content: center;
    gap: 15px;
    margin-bottom: 20px;
}

.btn-secondary, .nav-btn, .flip-btn {
    background: var(--bg-secondary);
    border: 2px solid var(--border-color);
    padding: 12px 24px;
    border-radius: 8px;
    cursor: pointer;
    font-size: 1rem;
    font-weight: 500;
    transition: var(--transition);
    color: var(--text-primary);
}

.btn-secondary:hover, .nav-btn:hover {
    border-color: var(--primary);
    transform: translateY(-2px);
}

.flip-btn {
    background: var(--primary);
    color: white;
    border-color: var(--primary);
    padding: 12px 32px;
    font-weight: bold;
}

.flip-btn:hover {
    background: var(--primary-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}

/* Assessment Controls */
.assessment-controls {
    text-align: center;
}

.assessment-controls.hidden {
    display: none;
}

.assessment-prompt {
    margin-bottom: 15px;
    color: var(--text-secondary);
    font-weight: 500;
}

.assessment-buttons {
    display: flex;
    justify-content: center;
    gap: 12px;
    flex-wrap: wrap;
}

.assess-btn {
    background: var(--bg-secondary);
    border: 2px solid var(--border-color);
    padding: 12px 20px;
    border-radius: 8px;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    flex-direction: column;
    align-items: center;
    min-width: 100px;
    color: var(--text-primary);
}

.assess-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}

.assess-btn.again {
    border-color: var(--danger);
}

.assess-btn.again:hover {
    background: var(--danger);
    color: white;
}

.assess-btn.hard {
    border-color: var(--warning);
}

.assess-btn.hard:hover {
    background: var(--warning);
    color: white;
}

.assess-btn.good {
    border-color: var(--success);
}

.assess-btn.good:hover {
    background: var(--success);
    color: white;
}

.assess-btn.easy {
    border-color: var(--primary);
}

.assess-btn.easy:hover {
    background: var(--primary);
    color: white;
}

.assess-label {
    font-weight: bold;
    margin-bottom: 4px;
}

.assess-interval {
    font-size: 0.8rem;
    opacity: 0.8;
}

.keyboard-hints {
    text-align: center;
    color: var(--text-muted);
    font-size: 0.85rem;
    margin-top: 20px;
}

/* Statistics Screen */
.stats-header {
    display: flex;
    align-items: center;
    gap: 20px;
    margin-bottom: 30px;
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
    margin-bottom: 40px;
}

.stat-card {
    background: var(--bg-secondary);
    padding: 30px;
    border-radius: 12px;
    text-align: center;
    box-shadow: var(--shadow);
}

.stat-value {
    font-size: 3rem;
    font-weight: bold;
    color: var(--primary);
    margin-bottom: 10px;
}

.stat-label {
    color: var(--text-secondary);
    font-size: 0.95rem;
}

/* Achievements */
.achievements {
    background: var(--bg-secondary);
    padding: 30px;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.achievements h3 {
    margin-bottom: 20px;
}

.achievement-list {
    display: flex;
    flex-direction: column;
    gap: 15px;
}

.achievement {
    display: flex;
    align-items: center;
    gap: 15px;
    padding: 15px;
    background: var(--bg-primary);
    border-radius: 8px;
    border: 2px solid transparent;
    transition: var(--transition);
}

.achievement.unlocked {
    border-color: var(--success);
    background: linear-gradient(135deg, rgba(72, 187, 120, 0.1) 0%, rgba(72, 187, 120, 0.05) 100%);
}

.achievement.locked {
    opacity: 0.5;
}

.achievement-icon {
    font-size: 2.5rem;
}

.achievement-title {
    font-weight: bold;
    margin-bottom: 4px;
}

.achievement-desc {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

/* Footer */
.footer {
    margin-top: 40px;
    padding: 20px;
    text-align: center;
    color: var(--text-muted);
    font-size: 0.9rem;
}

/* Responsive Design */
@media (max-width: 768px) {
    .header h1 {
        font-size: 1.4rem;
    }

    .welcome-content {
        padding: 20px;
    }

    .level-cards {
        grid-template-columns: 1fr;
    }

    .flashcard {
        height: 380px;
    }

    .card-content {
        font-size: 2rem;
    }

    .assessment-buttons {
        gap: 8px;
    }

    .assess-btn {
        min-width: 80px;
        padding: 10px 12px;
    }
}

/* Audio Controls */
.card-content-wrapper {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 20px;
    width: 100%;
}

.speaker-btn {
    background: var(--primary);
    border: none;
    padding: 12px;
    border-radius: 50%;
    font-size: 1.5rem;
    cursor: pointer;
    transition: var(--transition);
    display: inline-flex;
    align-items: center;
    justify-content: center;
    min-width: 50px;
    min-height: 50px;
    box-shadow: var(--shadow);
}

.speaker-btn:hover {
    background: var(--primary-dark);
    transform: scale(1.1);
}

.speaker-btn:active {
    transform: scale(0.95);
}

.speaker-btn.playing {
    background: var(--success);
    animation: pulse 1s infinite;
}

.speaker-btn:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

.speaker-icon {
    display: block;
    line-height: 1;
}

@keyframes pulse {
    0%, 100% {
        transform: scale(1);
    }
    50% {
        transform: scale(1.05);
    }
}

/* Audio toggle in header */
#audioToggle {
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    padding: 8px 16px;
    border-radius: 8px;
    font-size: 1.2rem;
    cursor: pointer;
    transition: var(--transition);
}

#audioToggle:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}

/* Responsive audio controls */
@media (max-width: 768px) {
    .speaker-btn {
        min-width: 45px;
        min-height: 45px;
        font-size: 1.3rem;
    }

    .card-content-wrapper {
        gap: 15px;
    }
}