/* style.css */

/* ==========================================
   Design Tokens & Variables
   ========================================== */
:root {
    /* Color Palette */
    --hue-primary: 250; /* Elegant Violet */
    --hue-success: 145; /* Soft Emerald Green */
    --hue-warning: 38;  /* Muted Amber Yellow */
    --hue-danger: 355;  /* Elegant Coral Red */

    --font-sans: 'Outfit', 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    
    /* Transition Times */
    --transition-fast: 0.2s ease;
    --transition-normal: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 0.6s cubic-bezier(0.4, 0, 0.2, 1);
    
    /* Layout Tokens */
    --border-radius-sm: 8px;
    --border-radius-md: 16px;
    --border-radius-lg: 24px;
    --border-radius-xl: 32px;
}

/* Light Theme Variables */
.theme-light {
    --bg-app: linear-gradient(135deg, #f5f7fb 0%, #e4e8f3 100%);
    --bg-sidebar: rgba(255, 255, 255, 0.7);
    --bg-card: rgba(255, 255, 255, 0.65);
    --bg-card-border: rgba(255, 255, 255, 0.5);
    
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --text-inverse: #ffffff;
    
    --shadow-sm: 0 4px 6px -1px rgba(0, 0, 0, 0.05), 0 2px 4px -1px rgba(0, 0, 0, 0.03);
    --shadow-md: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -2px rgba(0, 0, 0, 0.04);
    --shadow-lg: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    
    --color-primary: hsl(var(--hue-primary), 75%, 55%);
    --color-primary-light: hsl(var(--hue-primary), 80%, 94%);
    
    /* Mastering States Colors */
    --color-mastered: hsl(var(--hue-success), 60%, 43%);
    --color-mastered-bg: hsl(var(--hue-success), 80%, 94%);
    --color-familiar: hsl(var(--hue-warning), 75%, 45%);
    --color-familiar-bg: hsl(var(--hue-warning), 90%, 93%);
    --color-unlearned: hsl(var(--hue-danger), 75%, 52%);
    --color-unlearned-bg: hsl(var(--hue-danger), 90%, 94%);

    --glass-blur: blur(16px);
    --glass-border: 1px solid rgba(255, 255, 255, 0.4);
}

/* Dark Theme Variables */
.theme-dark {
    --bg-app: linear-gradient(135deg, #0f172a 0%, #1e1b4b 100%);
    --bg-sidebar: rgba(15, 23, 42, 0.6);
    --bg-card: rgba(30, 41, 59, 0.55);
    --bg-card-border: rgba(255, 255, 255, 0.07);
    
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --text-inverse: #0f172a;
    
    --shadow-sm: 0 4px 6px -1px rgba(0, 0, 0, 0.2);
    --shadow-md: 0 10px 15px -3px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 20px 25px -5px rgba(0, 0, 0, 0.4);
    
    --color-primary: hsl(var(--hue-primary), 85%, 65%);
    --color-primary-light: hsl(var(--hue-primary), 35%, 15%);
    
    /* Mastering States Colors */
    --color-mastered: hsl(var(--hue-success), 65%, 50%);
    --color-mastered-bg: hsl(var(--hue-success), 40%, 12%);
    --color-familiar: hsl(var(--hue-warning), 85%, 55%);
    --color-familiar-bg: hsl(var(--hue-warning), 45%, 13%);
    --color-unlearned: hsl(var(--hue-danger), 85%, 60%);
    --color-unlearned-bg: hsl(var(--hue-danger), 40%, 14%);

    --glass-blur: blur(20px);
    --glass-border: 1px solid rgba(255, 255, 255, 0.08);
}

/* ==========================================
   Global Reset & Base Layout
   ========================================== */
* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    user-select: none;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: var(--font-sans);
    background: var(--bg-app);
    color: var(--text-primary);
    min-height: 100vh;
    overflow: hidden;
    position: relative;
    display: flex;
    justify-content: center;
    align-items: center;
    transition: background var(--transition-slow);
}

/* Dynamic background glow balls */
.bg-glow {
    position: absolute;
    border-radius: 50%;
    filter: blur(120px);
    z-index: -1;
    opacity: 0.35;
    pointer-events: none;
    transition: all var(--transition-slow);
}
.bg-glow-1 {
    width: 40vw;
    height: 40vw;
    background: radial-gradient(circle, hsl(var(--hue-primary), 80%, 65%) 0%, transparent 70%);
    top: -10vw;
    left: -10vw;
}
.bg-glow-2 {
    width: 35vw;
    height: 35vw;
    background: radial-gradient(circle, hsl(var(--hue-success), 80%, 65%) 0%, transparent 70%);
    bottom: -5vw;
    right: -5vw;
}

/* Main Layout Container */
.app-container {
    width: 94vw;
    height: 90vh;
    max-width: 1400px;
    max-height: 900px;
    display: grid;
    grid-template-columns: 340px 1fr;
    gap: 20px;
    background: var(--bg-card);
    backdrop-filter: var(--glass-blur);
    border: var(--glass-border);
    border-radius: var(--border-radius-lg);
    box-shadow: var(--shadow-lg);
    overflow: hidden;
    transition: all var(--transition-normal);
}

/* ==========================================
   Sidebar Styling
   ========================================== */
.sidebar {
    background: var(--bg-sidebar);
    border-right: var(--glass-border);
    display: flex;
    flex-direction: column;
    overflow-y: auto;
    height: 100%;
}

.app-header {
    padding: 24px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--bg-card-border);
}

.logo {
    display: flex;
    align-items: center;
    gap: 12px;
    font-family: 'Outfit', sans-serif;
    font-size: 1.25rem;
    font-weight: 800;
    color: var(--color-primary);
}

.logo i {
    font-size: 1.5rem;
}

/* Interactive Controls */
.stats-section, .control-section, .segments-section {
    padding: 20px 24px;
    border-bottom: 1px solid var(--bg-card-border);
}

.stats-section h3, .control-section h3, .segments-section h3 {
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-secondary);
    margin-bottom: 16px;
    font-weight: 600;
}

.stats-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
    margin-bottom: 16px;
}

.stat-card {
    padding: 12px;
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid var(--bg-card-border);
    border-radius: var(--border-radius-md);
    display: flex;
    flex-direction: column;
    cursor: pointer;
    transition: all var(--transition-fast);
}
.stat-card:hover, .stat-card.active {
    transform: translateY(-2px);
    background: var(--color-primary-light);
    border-color: var(--color-primary);
}

.stat-card.active[data-group="mastered"] { background: var(--color-mastered-bg); border-color: var(--color-mastered); }
.stat-card.active[data-group="familiar"] { background: var(--color-familiar-bg); border-color: var(--color-familiar); }
.stat-card.active[data-group="unlearned"] { background: var(--color-unlearned-bg); border-color: var(--color-unlearned); }

.stat-num {
    font-size: 1.5rem;
    font-weight: 700;
    font-family: 'Outfit', sans-serif;
}
.stat-label {
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-top: 4px;
}

/* Stat color variants */
.stat-green .stat-num { color: var(--color-mastered); }
.stat-yellow .stat-num { color: var(--color-familiar); }
.stat-red .stat-num { color: var(--color-unlearned); }

/* Progress bar */
.progress-bar-container {
    height: 8px;
    background: var(--bg-card-border);
    border-radius: 4px;
    overflow: hidden;
}
.progress-bar-fill {
    height: 100%;
    background: var(--color-primary);
    border-radius: 4px;
    transition: width var(--transition-normal);
}

/* Control Select Inputs */
.select-group {
    display: flex;
    flex-direction: column;
    gap: 8px;
    margin-bottom: 16px;
}
.select-group label {
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--text-primary);
}
.select-group select {
    padding: 12px;
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid var(--bg-card-border);
    border-radius: var(--border-radius-md);
    color: var(--text-primary);
    font-family: var(--font-sans);
    font-size: 0.9rem;
    outline: none;
    cursor: pointer;
    transition: all var(--transition-fast);
}
.select-group select:focus {
    border-color: var(--color-primary);
    box-shadow: 0 0 0 2px var(--color-primary-light);
}

/* Segment list */
.segments-list {
    display: flex;
    flex-direction: column;
    gap: 8px;
    max-height: 250px;
    overflow-y: auto;
    padding-right: 4px;
}
.segment-item {
    padding: 12px 16px;
    background: rgba(255, 255, 255, 0.03);
    border: 1px solid var(--bg-card-border);
    border-radius: var(--border-radius-md);
    display: flex;
    justify-content: space-between;
    align-items: center;
    cursor: pointer;
    font-size: 0.85rem;
    transition: all var(--transition-fast);
}
.segment-item:hover {
    background: var(--bg-card-border);
    transform: translateX(4px);
}
.segment-item.active {
    background: var(--color-primary);
    color: var(--text-inverse);
    border-color: var(--color-primary);
}
.segment-item .count-badge {
    background: var(--bg-card-border);
    padding: 2px 8px;
    border-radius: 12px;
    font-size: 0.75rem;
    font-weight: 600;
}
.segment-item.active .count-badge {
    background: rgba(255, 255, 255, 0.2);
    color: var(--text-inverse);
}

/* Custom Scrollbar for Sidebar and Segments */
.sidebar::-webkit-scrollbar, .segments-list::-webkit-scrollbar {
    width: 6px;
}
.sidebar::-webkit-scrollbar-thumb, .segments-list::-webkit-scrollbar-thumb {
    background: rgba(0, 0, 0, 0.15);
    border-radius: 3px;
}
.theme-dark .sidebar::-webkit-scrollbar-thumb, .theme-dark .segments-list::-webkit-scrollbar-thumb {
    background: rgba(255, 255, 255, 0.15);
}

/* ==========================================
   Main Content Layout
   ========================================== */
.main-content {
    display: flex;
    flex-direction: column;
    height: 100%;
    padding: 24px;
    position: relative;
}

.top-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 24px;
}

.current-info {
    display: flex;
    align-items: center;
    gap: 12px;
}
.current-info span:first-child {
    font-size: 1.25rem;
    font-weight: 700;
    font-family: 'Outfit', sans-serif;
}
.badge {
    background: var(--color-primary-light);
    color: var(--color-primary);
    padding: 4px 10px;
    border-radius: var(--border-radius-sm);
    font-weight: 600;
    font-size: 0.8rem;
}

/* ==========================================
   Word Card & 3D Flipping Architecture
   ========================================== */
.card-area {
    flex-grow: 1;
    display: flex;
    justify-content: center;
    align-items: center;
    perspective: 1200px; /* Crucial for 3D flip depth */
    margin-bottom: 24px;
}

.word-card-wrapper {
    width: 100%;
    max-width: 580px;
    height: 380px;
    position: relative;
}

.word-card {
    width: 100%;
    height: 100%;
    position: absolute;
    transform-style: preserve-3d;
    transition: transform var(--transition-slow);
    cursor: pointer;
}

/* Flip state */
.word-card.flipped {
    transform: rotateY(180deg);
}

.card-face {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden; /* Hides back when front is shown */
    border-radius: var(--border-radius-xl);
    padding: 36px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    box-shadow: var(--shadow-md);
    border: var(--glass-border);
    transition: box-shadow var(--transition-fast);
}

.card-front {
    background: linear-gradient(135deg, rgba(255, 255, 255, 0.8) 0%, rgba(255, 255, 255, 0.45) 100%);
}
.theme-dark .card-front {
    background: linear-gradient(135deg, rgba(30, 41, 59, 0.7) 0%, rgba(15, 23, 42, 0.5) 100%);
}

.card-back {
    background: linear-gradient(135deg, rgba(255, 255, 255, 0.9) 0%, rgba(241, 245, 249, 0.8) 100%);
    transform: rotateY(180deg); /* Start turned around */
}
.theme-dark .card-back {
    background: linear-gradient(135deg, rgba(30, 41, 59, 0.95) 0%, rgba(15, 23, 42, 0.85) 100%);
}

.word-card:hover .card-face {
    box-shadow: var(--shadow-lg);
}

/* Card internals */
.card-header {
    display: flex;
    justify-content: flex-end;
}
.freq-badge {
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--text-secondary);
    background: rgba(0, 0, 0, 0.04);
    padding: 6px 12px;
    border-radius: 12px;
    display: flex;
    align-items: center;
    gap: 6px;
}
.theme-dark .freq-badge {
    background: rgba(255, 255, 255, 0.05);
}
.freq-badge strong {
    color: var(--color-primary);
}

.card-body {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
    flex-grow: 1;
}

.word-spelling {
    font-family: 'Outfit', sans-serif;
    font-size: 4rem;
    font-weight: 800;
    letter-spacing: -0.02em;
    color: var(--text-primary);
    margin-bottom: 20px;
}

.word-spelling-back {
    font-family: 'Outfit', sans-serif;
    font-size: 2.25rem;
    font-weight: 700;
    color: var(--color-primary);
    margin-bottom: 12px;
}

.translation-box {
    width: 100%;
    max-height: 140px;
    overflow-y: auto;
    padding: 0 10px;
}
.translation-box p {
    font-size: 1.25rem;
    line-height: 1.6;
    color: var(--text-primary);
}

.card-footer-tip {
    font-size: 0.8rem;
    color: var(--text-secondary);
    text-align: center;
    letter-spacing: 0.05em;
    text-transform: uppercase;
}

/* ==========================================
   Buttons and Action Bars
   ========================================== */
.btn-icon {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    border: 1px solid var(--bg-card-border);
    background: rgba(255, 255, 255, 0.1);
    color: var(--text-primary);
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all var(--transition-fast);
    outline: none;
}
.btn-icon:hover {
    background: var(--color-primary-light);
    color: var(--color-primary);
    border-color: var(--color-primary);
    transform: scale(1.05);
}

.btn-text {
    background: none;
    border: none;
    color: var(--text-secondary);
    font-family: var(--font-sans);
    font-size: 0.85rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 6px;
    padding: 6px 12px;
    border-radius: var(--border-radius-sm);
    transition: all var(--transition-fast);
}
.btn-text:hover {
    color: var(--color-primary);
    background: var(--color-primary-light);
}

.btn-play {
    border: none;
    background: var(--color-primary-light);
    color: var(--color-primary);
    padding: 10px 20px;
    border-radius: 20px;
    font-family: var(--font-sans);
    font-size: 0.95rem;
    font-weight: 600;
    display: flex;
    align-items: center;
    gap: 8px;
    cursor: pointer;
    transition: all var(--transition-fast);
}
.btn-play:hover {
    background: var(--color-primary);
    color: var(--text-inverse);
    transform: scale(1.05);
}

/* Bottom Action Bar */
.action-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 16px;
}

.nav-buttons button {
    padding: 14px 24px;
    border-radius: var(--border-radius-md);
    font-family: var(--font-sans);
    font-size: 0.95rem;
    font-weight: 600;
    border: 1px solid var(--bg-card-border);
    background: rgba(255, 255, 255, 0.1);
    color: var(--text-primary);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 8px;
    transition: all var(--transition-fast);
}
.nav-buttons button:hover {
    background: var(--bg-card-border);
    transform: translateY(-2px);
}

.mark-buttons {
    display: flex;
    gap: 16px;
}

.btn-mark {
    padding: 14px 28px;
    border-radius: var(--border-radius-md);
    font-family: var(--font-sans);
    font-weight: 600;
    font-size: 0.95rem;
    border: none;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 8px;
    transition: all var(--transition-fast);
}
.btn-mark:hover {
    transform: translateY(-4px);
    box-shadow: 0 8px 20px -6px currentColor;
}
.btn-mark:active {
    transform: translateY(-1px);
}

.mark-red {
    background: var(--color-unlearned-bg);
    color: var(--color-unlearned);
}
.mark-red.active {
    background: var(--color-unlearned);
    color: var(--text-inverse);
}

.mark-yellow {
    background: var(--color-familiar-bg);
    color: var(--color-familiar);
}
.mark-yellow.active {
    background: var(--color-familiar);
    color: var(--text-inverse);
}

.mark-green {
    background: var(--color-mastered-bg);
    color: var(--color-mastered);
}
.mark-green.active {
    background: var(--color-mastered);
    color: var(--text-inverse);
}

/* ==========================================
   Modal Dialog for Keyboard Shortcuts
   ========================================== */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    background: rgba(0, 0, 0, 0.45);
    backdrop-filter: blur(8px);
    z-index: 100;
    display: flex;
    justify-content: center;
    align-items: center;
    opacity: 0;
    pointer-events: none;
    transition: opacity var(--transition-normal);
}
.modal-overlay.open {
    opacity: 1;
    pointer-events: auto;
}

.modal {
    background: var(--bg-card);
    border: var(--glass-border);
    box-shadow: var(--shadow-lg);
    border-radius: var(--border-radius-lg);
    width: 90%;
    max-width: 460px;
    overflow: hidden;
    transform: scale(0.9);
    transition: transform var(--transition-normal);
}
.modal-overlay.open .modal {
    transform: scale(1);
}

.modal-header {
    padding: 20px 24px;
    border-bottom: 1px solid var(--bg-card-border);
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.modal-header h3 {
    font-size: 1.1rem;
    font-weight: 700;
}
.btn-close {
    background: none;
    border: none;
    font-size: 1.75rem;
    color: var(--text-secondary);
    cursor: pointer;
}
.btn-close:hover {
    color: var(--text-primary);
}

.modal-body {
    padding: 24px;
}

.shortcut-table {
    width: 100%;
    border-collapse: collapse;
}
.shortcut-table tr {
    border-bottom: 1px solid var(--bg-card-border);
}
.shortcut-table tr:last-child {
    border-bottom: none;
}
.shortcut-table td {
    padding: 12px 6px;
    font-size: 0.95rem;
}
.shortcut-table td:first-child {
    width: 40%;
}
kbd {
    background: rgba(0,0,0,0.06);
    border: 1px solid rgba(0,0,0,0.12);
    border-radius: 4px;
    padding: 2px 6px;
    font-family: monospace;
    font-size: 0.85rem;
    box-shadow: 0 1px 0 rgba(0,0,0,0.1);
}
.theme-dark kbd {
    background: rgba(255,255,255,0.08);
    border-color: rgba(255,255,255,0.15);
}

/* ==========================================
   Responsive Adaptations
   ========================================== */
@media (max-width: 992px) {
    .app-container {
        grid-template-columns: 1fr;
        height: 96vh;
        width: 96vw;
    }
    
    .sidebar {
        display: none; /* In a real app we might have a hamburger drawer, but here we can toggle visible/hidden classes */
    }
    .sidebar.mobile-open {
        display: flex;
        position: fixed;
        top: 0;
        left: 0;
        width: 80vw;
        height: 100%;
        z-index: 50;
        box-shadow: var(--shadow-lg);
    }
}

@media (max-width: 576px) {
    .main-content {
        padding: 16px;
    }
    .word-card-wrapper {
        height: 320px;
    }
    .word-spelling {
        font-size: 3rem;
    }
    .action-footer {
        flex-direction: column;
        gap: 12px;
    }
    .mark-buttons {
        width: 100%;
        justify-content: space-between;
    }
    .btn-mark {
        flex-grow: 1;
        padding: 12px 10px;
        justify-content: center;
        font-size: 0.85rem;
    }
    .nav-buttons {
        width: 100%;
        display: flex;
        justify-content: space-between;
    }
    .nav-buttons button {
        width: 48%;
        justify-content: center;
    }
}