/* リセットとベース設定 */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary-color: #4a69bd;
    --secondary-color: #6c5ce7;
    --success-color: #00b894;
    --danger-color: #d63031;
    --warning-color: #fdcb6e;
    --text-primary: #2d3436;
    --text-secondary: #636e72;
    --bg-primary: #ffffff;
    --bg-secondary: #f5f6fa;
    --border-color: #dfe6e9;
    --shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
    --shadow-hover: 0 4px 16px rgba(0, 0, 0, 0.15);
    --radius: 8px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--bg-secondary);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* ヘッダー */
header {
    background-color: var(--bg-primary);
    box-shadow: var(--shadow);
    position: sticky;
    top: 0;
    z-index: 100;
}

header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 20px;
}

h1 {
    display: flex;
    align-items: center;
    gap: 10px;
    font-size: 1.5rem;
    color: var(--primary-color);
}

.logo {
    font-size: 2rem;
}

.lang-selector select {
    padding: 0.5rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    background-color: var(--bg-primary);
    cursor: pointer;
    font-size: 0.9rem;
}

/* メインコンテンツ */
main {
    flex: 1;
    padding: 2rem 0;
}

.card {
    background-color: var(--bg-primary);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 2rem;
    margin-bottom: 2rem;
    transition: box-shadow 0.3s ease;
}

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

/* ボタン */
.btn {
    padding: 0.75rem 1.5rem;
    border: none;
    border-radius: var(--radius);
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.3s ease;
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    text-decoration: none;
    color: white;
}

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

.btn-primary:hover {
    background-color: #3c5aa6;
    transform: translateY(-2px);
}

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

.btn-secondary:hover {
    background-color: #57606f;
}

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

.btn-danger:hover {
    background-color: #c0392b;
}

.btn-small {
    padding: 0.5rem 1rem;
    font-size: 0.875rem;
}

/* デッキ一覧 */
.deck-controls {
    display: flex;
    gap: 1rem;
    margin-bottom: 2rem;
    flex-wrap: wrap;
}

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

.deck-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1.5rem;
    background-color: var(--bg-secondary);
    border-radius: var(--radius);
    transition: all 0.3s ease;
}

.deck-item:hover {
    transform: translateX(5px);
    box-shadow: var(--shadow);
}

.deck-info h3 {
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

.deck-info p {
    color: var(--text-secondary);
    font-size: 0.875rem;
}

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

/* 学習画面 */
.progress-bar {
    width: 100%;
    height: 8px;
    background-color: var(--border-color);
    border-radius: var(--radius);
    margin-bottom: 2rem;
    position: relative;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background-color: var(--primary-color);
    transition: width 0.3s ease;
}

.progress-text {
    position: absolute;
    top: -25px;
    right: 0;
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.flashcard {
    min-height: 300px;
    margin: 2rem 0;
    perspective: 1000px;
}

.flashcard-content {
    position: relative;
    width: 100%;
    height: 100%;
    text-align: center;
    transition: transform 0.6s;
    transform-style: preserve-3d;
}

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

.card-side {
    position: absolute;
    width: 100%;
    min-height: 300px;
    backface-visibility: hidden;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 2rem;
    background-color: var(--bg-secondary);
    border-radius: var(--radius);
    border: 2px solid var(--border-color);
}

#card-back {
    transform: rotateY(180deg);
}

.card-side p {
    font-size: 1.25rem;
    line-height: 1.8;
}

.study-controls {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 1rem;
    margin: 2rem 0;
}

.difficulty-buttons {
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
    justify-content: center;
}

.difficulty-btn[data-difficulty="1"] {
    background-color: var(--danger-color);
}

.difficulty-btn[data-difficulty="2"] {
    background-color: var(--warning-color);
    color: var(--text-primary);
}

.difficulty-btn[data-difficulty="3"] {
    background-color: var(--success-color);
}

.difficulty-btn[data-difficulty="4"] {
    background-color: var(--primary-color);
}

/* 編集画面 */
.input {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    font-size: 1rem;
    transition: border-color 0.3s ease;
}

.input:focus {
    outline: none;
    border-color: var(--primary-color);
}

.card-editor {
    margin: 2rem 0;
}

.card-editor h3 {
    margin-bottom: 1rem;
}

.cards-list {
    margin-top: 1rem;
}

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

.card-inputs {
    display: flex;
    gap: 1rem;
    flex: 1;
}

.card-front,
.card-back {
    flex: 1;
}

.edit-controls {
    display: flex;
    gap: 1rem;
    justify-content: flex-end;
    margin-top: 2rem;
}

/* 統計 */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1.5rem;
    margin-top: 1.5rem;
}

.stat-item {
    text-align: center;
    padding: 1.5rem;
    background-color: var(--bg-secondary);
    border-radius: var(--radius);
    transition: transform 0.3s ease;
}

.stat-item:hover {
    transform: translateY(-5px);
}

.stat-value {
    display: block;
    font-size: 2rem;
    font-weight: bold;
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

.stat-label {
    color: var(--text-secondary);
    font-size: 0.875rem;
}

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

.modal-content {
    background-color: var(--bg-primary);
    padding: 2rem;
    border-radius: var(--radius);
    max-width: 500px;
    width: 90%;
    position: relative;
}

.close {
    position: absolute;
    top: 1rem;
    right: 1rem;
    font-size: 1.5rem;
    cursor: pointer;
    color: var(--text-secondary);
}

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

/* フッター */
footer {
    background-color: var(--bg-primary);
    text-align: center;
    padding: 1rem;
    margin-top: auto;
    border-top: 1px solid var(--border-color);
}

footer p {
    color: var(--text-secondary);
    font-size: 0.875rem;
}

/* ユーティリティ */
.hidden {
    display: none !important;
}

.empty-message {
    text-align: center;
    color: var(--text-secondary);
    padding: 2rem;
}

/* レスポンシブ */
@media (max-width: 768px) {
    .container {
        padding: 0 15px;
    }
    
    .card {
        padding: 1.5rem;
    }
    
    .deck-item {
        flex-direction: column;
        align-items: flex-start;
        gap: 1rem;
    }
    
    .deck-actions {
        width: 100%;
    }
    
    .card-inputs {
        flex-direction: column;
    }
    
    .difficulty-buttons {
        width: 100%;
    }
    
    .difficulty-btn {
        flex: 1;
    }
    
    .stats-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 480px) {
    h1 {
        font-size: 1.25rem;
    }
    
    .logo {
        font-size: 1.5rem;
    }
    
    .btn {
        padding: 0.5rem 1rem;
        font-size: 0.875rem;
    }
    
    .stats-grid {
        grid-template-columns: 1fr;
    }
}

/* アニメーション */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.card {
    animation: fadeIn 0.5s ease;
}

/* ダークモード対応 */
@media (prefers-color-scheme: dark) {
    :root {
        --text-primary: #dfe6e9;
        --text-secondary: #b2bec3;
        --bg-primary: #2d3436;
        --bg-secondary: #1e272e;
        --border-color: #485460;
    }
    
    .btn-secondary {
        background-color: #485460;
    }
    
    .input {
        background-color: var(--bg-secondary);
        color: var(--text-primary);
    }
}