:root {
    --bg-dark: #0f172a;
    --bg-card: rgba(30, 41, 59, 0.7);
    --text-main: #f8fafc;
    --text-muted: #94a3b8;
    
    --primary: #6366f1;
    --primary-hover: #4f46e5;
    --secondary: #334155;
    --secondary-hover: #475569;
    --success: #10b981;
    --success-hover: #059669;
    --danger: #ef4444;
    --danger-hover: #dc2626;
    --warning: #f59e0b;
    --warning-hover: #d97706;
    
    --font-heading: 'Outfit', sans-serif;
    --font-body: 'Inter', sans-serif;
}

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

body {
    background-color: var(--bg-dark);
    background-image: 
        radial-gradient(at 0% 0%, hsla(253,16%,7%,1) 0, transparent 50%), 
        radial-gradient(at 50% 0%, hsla(225,39%,30%,0.2) 0, transparent 50%), 
        radial-gradient(at 100% 0%, hsla(339,49%,30%,0.2) 0, transparent 50%);
    background-attachment: fixed;
    color: var(--text-main);
    font-family: var(--font-body);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    -webkit-font-smoothing: antialiased;
}

#app {
    width: 100%;
    max-width: 480px;
    height: 100vh;
    height: 100dvh;
    position: relative;
    overflow: hidden;
    display: flex;
    flex-direction: column;
}

.screen {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    display: flex;
    flex-direction: column;
    padding: 1.5rem;
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.3s ease, transform 0.3s ease;
    transform: translateX(20px);
    overflow-y: auto;
}

.screen.active {
    opacity: 1;
    pointer-events: all;
    transform: translateX(0);
}

h1, h2, h3 {
    font-family: var(--font-heading);
    font-weight: 700;
}

header {
    margin-bottom: 2rem;
    text-align: center;
}

header h1 {
    font-size: 2.2rem;
    background: linear-gradient(135deg, #a78bfa, #818cf8, #38bdf8);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    margin-bottom: 0.5rem;
}

header p {
    color: var(--text-muted);
    font-size: 0.95rem;
}

.header-nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 1.5rem;
    text-align: left;
}

.header-nav h2 {
    font-size: 1.2rem;
    margin: 0;
}

.btn-icon {
    background: rgba(255, 255, 255, 0.1);
    border: none;
    color: white;
    width: 40px;
    height: 40px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.2rem;
    cursor: pointer;
    backdrop-filter: blur(10px);
    transition: background 0.2s;
}

.btn-icon:hover {
    background: rgba(255, 255, 255, 0.2);
}

/* Stats Card */
.stats-card {
    background: var(--bg-card);
    backdrop-filter: blur(16px);
    border: 1px solid rgba(255,255,255,0.1);
    border-radius: 1rem;
    padding: 1.5rem;
    display: flex;
    justify-content: space-around;
    margin-bottom: 2rem;
    box-shadow: 0 10px 30px -10px rgba(0,0,0,0.5);
}

.stat-item {
    display: flex;
    flex-direction: column;
    align-items: center;
}

.stat-value {
    font-size: 2rem;
    font-weight: 800;
    font-family: var(--font-heading);
}

.text-success { color: var(--success); }
.text-danger { color: var(--danger); }

.stat-label {
    color: var(--text-muted);
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-top: 0.25rem;
    text-align: center;
}

/* Settings Group */
.settings-group {
    background: var(--bg-card);
    border-radius: 1rem;
    padding: 1rem;
    margin-bottom: 1.5rem;
    border: 1px solid rgba(255,255,255,0.05);
}

.settings-group label {
    display: block;
    margin-bottom: 0.75rem;
    font-weight: 600;
    color: #cbd5e1;
}

.radio-group {
    display: flex;
    gap: 0.5rem;
}

.radio-group input[type="radio"] {
    display: none;
}

.radio-group label {
    flex: 1;
    text-align: center;
    padding: 0.75rem;
    background: rgba(255,255,255,0.05);
    border-radius: 0.5rem;
    cursor: pointer;
    transition: all 0.2s;
    font-size: 0.9rem;
    margin: 0;
    border: 1px solid transparent;
}

.radio-group input[type="radio"]:checked + label {
    background: rgba(99, 102, 241, 0.2);
    border-color: var(--primary);
    color: white;
}

/* Buttons */
.btn {
    font-family: var(--font-heading);
    font-weight: 600;
    border: none;
    border-radius: 0.75rem;
    padding: 1rem;
    font-size: 1rem;
    cursor: pointer;
    transition: transform 0.1s, background 0.2s, box-shadow 0.2s;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    color: white;
}

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

.btn-block {
    width: 100%;
    margin-bottom: 1rem;
}

.btn-lg {
    padding: 1.25rem;
    font-size: 1.1rem;
}

.btn-sm {
    padding: 0.75rem;
    font-size: 0.9rem;
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary), var(--primary-hover));
    box-shadow: 0 4px 15px rgba(99, 102, 241, 0.4);
}

.btn-secondary {
    background: var(--secondary);
}
.btn-secondary:hover { background: var(--secondary-hover); }

.btn-warning {
    background: var(--warning);
    box-shadow: 0 4px 15px rgba(245, 158, 11, 0.4);
    color: #fff;
}

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

.btn-success {
    background: var(--success);
}

.mt-4 { margin-top: 1.5rem; }

/* Category List */
.category-list {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
    overflow-y: auto;
    padding-bottom: 2rem;
}

.category-item {
    background: var(--bg-card);
    border: 1px solid rgba(255,255,255,0.05);
    padding: 1rem;
    border-radius: 0.75rem;
    cursor: pointer;
    transition: background 0.2s, transform 0.2s;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.category-item:hover {
    background: rgba(255,255,255,0.1);
    transform: translateY(-2px);
}

.cat-name { font-weight: 600; font-size: 0.95rem; }
.cat-count {
    background: rgba(255,255,255,0.1);
    padding: 0.25rem 0.5rem;
    border-radius: 1rem;
    font-size: 0.8rem;
    color: var(--text-muted);
    white-space: nowrap;
    margin-left: 0.5rem;
}

/* Practice Screen */
.practice-stats {
    display: flex;
    gap: 0.5rem;
}

.badge {
    padding: 0.25rem 0.5rem;
    border-radius: 1rem;
    font-weight: 700;
    font-size: 0.85rem;
}

.badge-success { background: rgba(16, 185, 129, 0.2); color: var(--success); }
.badge-danger { background: rgba(239, 68, 68, 0.2); color: var(--danger); }

.progress-text {
    font-weight: 600;
    color: var(--text-muted);
}

/* Flashcard */
.flashcard-container {
    flex: 1;
    perspective: 1000px;
    margin-bottom: 2rem;
    display: flex;
    align-items: center;
    justify-content: center;
}

.flashcard {
    width: 100%;
    height: 100%;
    max-height: 440px;
    background-color: transparent;
    cursor: pointer;
}

.flashcard-inner {
    position: relative;
    width: 100%;
    height: 100%;
    text-align: center;
    transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
    transform-style: preserve-3d;
}

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

.flashcard-front, .flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    -webkit-backface-visibility: hidden;
    backface-visibility: hidden;
    border-radius: 1.5rem;
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background: linear-gradient(145deg, rgba(30,41,59,0.95), rgba(15,23,42,0.95));
    border: 1px solid rgba(255,255,255,0.1);
    box-shadow: 0 20px 40px -10px rgba(0,0,0,0.5), inset 0 1px 0 rgba(255,255,255,0.1);
    backdrop-filter: blur(10px);
}

.flashcard-back {
    transform: rotateY(180deg);
    justify-content: space-evenly;
}

.card-title {
    font-size: 2.2rem;
    margin-bottom: 0.5rem;
    background: linear-gradient(135deg, #f8fafc, #94a3b8);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    word-break: break-word;
    line-height: 1.2;
}

.card-subtitle {
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.1em;
    font-size: 0.9rem;
}

.verb-info {
    width: 100%;
    display: flex;
    flex-direction: column;
    align-items: center;
    margin-bottom: 0.5rem;
}

.verb-info:last-child { margin-bottom: 0; }

.verb-info .label {
    font-size: 0.75rem;
    color: var(--primary);
    text-transform: uppercase;
    letter-spacing: 0.1em;
    font-weight: 700;
    margin-bottom: 0.25rem;
}

.verb-info h3 {
    font-size: 1.3rem;
    color: var(--text-main);
    margin: 0;
}

/* Controls */
.controls {
    margin-bottom: 1rem;
    min-height: 60px;
}

.action-buttons {
    display: flex;
    gap: 1rem;
}

.action-buttons .btn {
    flex: 1;
    margin-bottom: 0;
}

/* End Screen */
.end-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
}

.end-content h2 {
    font-size: 2.2rem;
    margin-bottom: 2rem;
    color: var(--primary);
}

.final-stats {
    display: flex;
    gap: 2rem;
    margin-bottom: 3rem;
}

.stat-circle {
    width: 120px;
    height: 120px;
    border-radius: 50%;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    background: rgba(255,255,255,0.05);
    border: 4px solid;
}

.stat-circle.success { border-color: var(--success); }
.stat-circle.danger { border-color: var(--danger); }

.stat-circle span {
    font-size: 2.5rem;
    font-weight: 800;
    font-family: var(--font-heading);
}

.stat-circle small {
    color: var(--text-muted);
    text-transform: uppercase;
    font-size: 0.8rem;
    letter-spacing: 0.05em;
}

@media (max-width: 380px) {
    .card-title { font-size: 1.8rem; }
    .verb-info h3 { font-size: 1.1rem; }
    .stat-circle { width: 100px; height: 100px; }
    .stat-circle span { font-size: 2rem; }
    .btn { padding: 0.8rem; font-size: 0.95rem; }
}