/* ============================================
   Languages - Adaptive Language Learning
   Modern, Mobile-First CSS
   ============================================ */

/* CSS Variables for theming */
:root {
    /* Colors */
    --color-bg-primary: #1a1a2e;
    --color-bg-secondary: #16213e;
    --color-bg-card: #0f3460;
    --color-accent: #4a90d9;
    --color-accent-hover: #5ba0e9;
    --color-text-primary: #eaeaea;
    --color-text-secondary: #a0a0a0;
    --color-text-muted: #6a6a6a;
    
    /* Rating colors */
    --color-hard: #e74c3c;
    --color-hard-hover: #c0392b;
    --color-normal: #f39c12;
    --color-normal-hover: #d68910;
    --color-easy: #27ae60;
    --color-easy-hover: #1e8449;
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-xxl: 3rem;
    
    /* Typography */
    --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
    --font-size-sm: 0.875rem;
    --font-size-md: 1rem;
    --font-size-lg: 1.25rem;
    --font-size-xl: 1.5rem;
    --font-size-xxl: 2rem;
    --font-size-card: 1.5rem;
    
    /* Border radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 1rem;
    --radius-xl: 1.5rem;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.2);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.4);
    --shadow-card: 0 8px 32px rgba(0, 0, 0, 0.3);
    
    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-normal: 250ms ease;
    --transition-slow: 400ms ease;
    
    /* Card dimensions */
    --card-max-width: 400px;
    --card-aspect-ratio: 3 / 4;
}

/* Reset & Base */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    -webkit-text-size-adjust: 100%;
    /* Background color for dynamic island/notch area on iOS */
    background-color: var(--color-bg-primary);
}

body {
    font-family: var(--font-family);
    background: linear-gradient(135deg, var(--color-bg-primary) 0%, var(--color-bg-secondary) 100%);
    color: var(--color-text-primary);
    min-height: 100vh;
    min-height: 100dvh;
    line-height: 1.5;
    overflow-x: hidden;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    /* iOS Safe Area Support */
    padding-top: env(safe-area-inset-top);
    padding-left: env(safe-area-inset-left);
    padding-right: env(safe-area-inset-right);
}

/* App container */
#app {
    min-height: 100vh;
    min-height: 100dvh;
    display: flex;
    flex-direction: column;
}

/* Screen management */
.screen {
    display: none;
    flex-direction: column;
    min-height: 100vh;
    min-height: 100dvh;
}

.screen.active {
    display: flex;
}

/* Container */
.container {
    width: 100%;
    max-width: 480px;
    margin: 0 auto;
    padding: var(--spacing-lg);
}

/* ============================================
   Typography
   ============================================ */

.app-title {
    font-size: var(--font-size-xxl);
    font-weight: 700;
    text-align: center;
    margin-bottom: var(--spacing-xs);
    background: linear-gradient(135deg, var(--color-accent) 0%, #a855f7 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.app-subtitle {
    font-size: var(--font-size-md);
    color: var(--color-text-secondary);
    text-align: center;
    margin-bottom: var(--spacing-xxl);
}

/* ============================================
   Form Elements
   ============================================ */

.setup-form {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

.form-group label {
    font-size: var(--font-size-sm);
    font-weight: 500;
    color: var(--color-text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.select-input {
    appearance: none;
    background-color: var(--color-bg-card);
    border: 2px solid transparent;
    border-radius: var(--radius-md);
    color: var(--color-text-primary);
    font-size: var(--font-size-md);
    padding: var(--spacing-md) var(--spacing-lg);
    padding-right: 2.5rem;
    cursor: pointer;
    transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='24' height='24' viewBox='0 0 24 24'%3E%3Cpath fill='%23a0a0a0' d='M7 10l5 5 5-5z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 0.75rem center;
    background-size: 1.5rem;
}

.select-input:focus {
    outline: none;
    border-color: var(--color-accent);
    box-shadow: 0 0 0 3px rgba(74, 144, 217, 0.2);
}

.select-input:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* ============================================
   Buttons
   ============================================ */

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    font-family: inherit;
    font-size: var(--font-size-md);
    font-weight: 600;
    padding: var(--spacing-md) var(--spacing-xl);
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    text-decoration: none;
    user-select: none;
    -webkit-tap-highlight-color: transparent;
}

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

.btn:focus-visible {
    outline: 3px solid var(--color-accent);
    outline-offset: 2px;
}

.btn-primary {
    background: linear-gradient(135deg, var(--color-accent) 0%, #6366f1 100%);
    color: white;
    box-shadow: var(--shadow-md);
}

.btn-primary:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-primary:active:not(:disabled) {
    transform: translateY(0);
}

.btn-secondary {
    background-color: var(--color-bg-card);
    color: var(--color-text-primary);
}

.btn-secondary:hover:not(:disabled) {
    background-color: var(--color-bg-secondary);
}

.btn-icon {
    padding: var(--spacing-sm);
    background: transparent;
    color: var(--color-text-secondary);
    border-radius: var(--radius-sm);
}

.btn-icon:hover {
    background-color: rgba(255, 255, 255, 0.1);
    color: var(--color-text-primary);
}

.btn-small {
    font-size: var(--font-size-sm);
    padding: var(--spacing-sm) var(--spacing-md);
}

.btn-text {
    background: transparent;
    color: var(--color-text-secondary);
    padding: var(--spacing-sm);
}

.btn-text:hover {
    color: var(--color-text-primary);
}

/* Rating buttons */
.rating-buttons {
    display: flex;
    gap: var(--spacing-md);
    justify-content: center;
    padding: var(--spacing-lg);
    padding-bottom: calc(var(--spacing-lg) + env(safe-area-inset-bottom));
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    background: linear-gradient(to top, var(--color-bg-primary) 0%, transparent 100%);
    padding-top: var(--spacing-xl);
}

.btn-rating {
    flex: 1;
    max-width: 100px;
    padding: var(--spacing-md) var(--spacing-sm);
    border-radius: var(--radius-lg);
    font-weight: 600;
    font-size: var(--font-size-md);
}

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

.btn-hard:hover:not(:disabled) {
    background-color: var(--color-hard-hover);
}

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

.btn-normal:hover:not(:disabled) {
    background-color: var(--color-normal-hover);
}

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

.btn-easy:hover:not(:disabled) {
    background-color: var(--color-easy-hover);
}

/* ============================================
   Learning Screen
   ============================================ */

.learning-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--spacing-md) var(--spacing-lg);
    padding-top: calc(var(--spacing-md) + env(safe-area-inset-top));
    background-color: transparent;
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    z-index: 10;
}

.btn-autoplay {
    opacity: 0.5;
    transition: opacity var(--transition-fast), color var(--transition-fast);
}

.btn-autoplay[aria-pressed="true"] {
    opacity: 1;
    color: var(--color-accent);
}

.btn-autoplay svg {
    display: none;
}

.btn-autoplay .icon-autoplay-off {
    display: block;
}

.btn-autoplay[aria-pressed="true"] .icon-autoplay-off {
    display: none;
}

.btn-autoplay[aria-pressed="true"] .icon-autoplay-on {
    display: block;
}

/* ============================================
   Flashcard
   ============================================ */

.card-container {
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-lg);
    padding-bottom: calc(120px + env(safe-area-inset-bottom));
    gap: var(--spacing-lg);
    cursor: pointer;
    -webkit-tap-highlight-color: transparent;
}

.flashcard {
    width: 100%;
    max-width: var(--card-max-width);
    min-height: 300px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-xl);
    background: linear-gradient(145deg, var(--color-bg-card) 0%, var(--color-bg-secondary) 100%);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-card);
    text-align: center;
    cursor: pointer;
    -webkit-tap-highlight-color: transparent;
    position: relative;
    outline: none;
}

.flashcard:focus-visible {
    outline: 3px solid var(--color-accent);
    outline-offset: 4px;
}

.card-text {
    font-size: var(--font-size-card);
    line-height: 1.4;
    word-break: break-word;
}

.card-question {
    color: var(--color-text-primary);
}

.card-question-wrapper {
    display: flex;
    align-items: flex-start;
    justify-content: center;
    gap: var(--spacing-sm);
    width: 100%;
}

.btn-speak {
    flex-shrink: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 32px;
    height: 32px;
    padding: 0;
    background: transparent;
    border: none;
    border-radius: var(--radius-md);
    color: var(--color-text-secondary);
    cursor: pointer;
    transition: color var(--transition-fast), background-color var(--transition-fast), transform var(--transition-fast);
    -webkit-tap-highlight-color: transparent;
}

.btn-speak:hover,
.btn-speak:focus {
    color: var(--color-accent);
    background-color: rgba(74, 144, 217, 0.1);
}

.btn-speak:active {
    transform: scale(0.9);
}

.btn-speak.speaking {
    color: var(--color-accent);
    animation: pulse-speak 1s ease-in-out infinite;
}

@keyframes pulse-speak {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.5; }
}

.card-answer {
    width: 100%;
    margin-top: var(--spacing-lg);
}

.answer-divider {
    width: 60%;
    height: 2px;
    background: linear-gradient(90deg, transparent, var(--color-accent), transparent);
    margin: 0 auto var(--spacing-lg);
}

.card-answer .card-text {
    color: var(--color-accent);
}

.card-hint {
    position: absolute;
    bottom: var(--spacing-lg);
    font-size: var(--font-size-sm);
    color: var(--color-text-muted);
    opacity: 0.7;
    transition: opacity var(--transition-fast);
}

/* Reveal Button */
.btn-reveal {
    position: fixed;
    bottom: calc(var(--spacing-lg) + env(safe-area-inset-bottom));
    left: 50%;
    transform: translateX(-50%);
    padding: var(--spacing-md) var(--spacing-xxl);
    min-height: 48px;
    min-width: 200px;
    font-size: var(--font-size-lg);
    font-weight: 600;
    color: var(--color-text-primary);
    background: var(--color-bg-card);
    border: 2px solid var(--color-accent);
    border-radius: var(--radius-lg);
    cursor: pointer;
    transition: all var(--transition-fast);
    z-index: 10;
}

.btn-reveal:hover,
.btn-reveal:focus {
    background: var(--color-accent);
    color: var(--color-bg-primary);
}

.btn-reveal:active {
    transform: scale(0.98);
}

/* Card entrance animation */
@keyframes cardSlideIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.flashcard.entering {
    animation: cardSlideIn 0.25s ease-out;
}

/* ============================================
   Modal
   ============================================ */

.modal {
    position: fixed;
    inset: 0;
    background-color: rgba(0, 0, 0, 0.7);
    display: flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-lg);
    z-index: 100;
    backdrop-filter: blur(4px);
}

.modal-content {
    background-color: var(--color-bg-card);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    width: 100%;
    max-width: 360px;
    text-align: center;
}

.modal-content h2 {
    font-size: var(--font-size-xl);
    margin-bottom: var(--spacing-lg);
}

.session-stats {
    margin-bottom: var(--spacing-xl);
    color: var(--color-text-secondary);
}

.session-stats p {
    margin-bottom: var(--spacing-sm);
}

.modal-content .btn {
    width: 100%;
    margin-bottom: var(--spacing-sm);
}

/* ============================================
   Offline Indicator
   ============================================ */

.offline-indicator {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    background-color: var(--color-hard);
    color: white;
    text-align: center;
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: var(--font-size-sm);
    z-index: 200;
    transform: translateY(100%);
    transition: transform var(--transition-normal);
}

.offline-indicator.visible {
    transform: translateY(0);
}

/* ============================================
   Install Prompt
   ============================================ */

.install-prompt {
    position: fixed;
    bottom: var(--spacing-lg);
    left: var(--spacing-lg);
    right: var(--spacing-lg);
    background-color: var(--color-bg-card);
    border-radius: var(--radius-lg);
    padding: var(--spacing-md);
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--spacing-md);
    box-shadow: var(--shadow-lg);
    z-index: 150;
    transform: translateY(150%);
    transition: transform var(--transition-normal);
}

.install-prompt.visible {
    transform: translateY(0);
}

.install-prompt p {
    font-size: var(--font-size-sm);
    flex: 1;
}

/* ============================================
   Notification Toast
   ============================================ */

.notification {
    position: fixed;
    top: var(--spacing-lg);
    left: 50%;
    transform: translateX(-50%) translateY(-150%);
    background-color: var(--color-bg-card);
    color: var(--color-text-primary);
    padding: var(--spacing-md) var(--spacing-lg);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    z-index: 250;
    transition: transform var(--transition-normal);
    max-width: calc(100% - var(--spacing-xl) * 2);
    text-align: center;
}

.notification.visible {
    transform: translateX(-50%) translateY(0);
}

.notification.success {
    background-color: var(--color-easy);
    color: white;
}

.notification.error {
    background-color: var(--color-hard);
    color: white;
}

.notification.info {
    background-color: var(--color-accent);
    color: white;
}

/* ============================================
   Utility Classes
   ============================================ */

.hidden {
    display: none !important;
}

.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* ============================================
   Loading State
   ============================================ */

.loading {
    position: relative;
    pointer-events: none;
}

.loading::after {
    content: '';
    position: absolute;
    inset: 0;
    background-color: rgba(0, 0, 0, 0.5);
    border-radius: inherit;
    display: flex;
    align-items: center;
    justify-content: center;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

.spinner {
    width: 24px;
    height: 24px;
    border: 3px solid var(--color-text-muted);
    border-top-color: var(--color-accent);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}

/* ============================================
   Loading Overlay
   ============================================ */

.loading-overlay {
    position: fixed;
    inset: 0;
    background: linear-gradient(135deg, var(--color-bg-primary) 0%, var(--color-bg-secondary) 100%);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
    z-index: 300;
    transition: opacity var(--transition-normal);
}

.loading-overlay.hidden {
    opacity: 0;
    pointer-events: none;
}

.loading-overlay .spinner {
    width: 40px;
    height: 40px;
    border-width: 4px;
}

.loading-overlay p {
    color: var(--color-text-secondary);
    font-size: var(--font-size-md);
}

/* ============================================
   Responsive Adjustments
   ============================================ */

@media (min-width: 768px) {
    :root {
        --font-size-card: 1.75rem;
        --card-max-width: 450px;
    }
    
    .container {
        padding: var(--spacing-xl);
    }
    
    .rating-buttons {
        gap: var(--spacing-lg);
    }
    
    .btn-rating {
        max-width: 140px;
    }
}

@media (min-width: 1024px) {
    :root {
        --font-size-card: 2rem;
    }
    
    .flashcard:hover .card-inner {
        box-shadow: var(--shadow-lg);
    }
}

/* Prefer reduced motion */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
    
    .card-inner {
        transition: none;
    }
}

/* Dark mode is default, but support light preference */
@media (prefers-color-scheme: light) {
    :root {
        --color-bg-primary: #f5f5f7;
        --color-bg-secondary: #e8e8ed;
        --color-bg-card: #ffffff;
        --color-text-primary: #1d1d1f;
        --color-text-secondary: #6e6e73;
        --color-text-muted: #aeaeb2;
        --shadow-card: 0 8px 32px rgba(0, 0, 0, 0.1);
    }
    
    html {
        /* Update dynamic island/notch background for light mode */
        background-color: var(--color-bg-primary);
    }
    
    body {
        background: linear-gradient(135deg, var(--color-bg-primary) 0%, var(--color-bg-secondary) 100%);
    }
}