:root {
    --primary-color: #3b82f6;
    --primary-hover: #2563eb;
    --success-color: #10b981;
    --error-color: #ef4444;
    --warning-color: #f59e0b;
    
    /* Light theme */
    --bg-primary: #ffffff;
    --bg-secondary: #f3f4f6;
    --bg-tertiary: #e5e7eb;
    --text-primary: #1f2937;
    --text-secondary: #6b7280;
    --border-color: #d1d5db;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.1);
}

.dark-theme {
    --bg-primary: #1f2937;
    --bg-secondary: #111827;
    --bg-tertiary: #374151;
    --text-primary: #f9fafb;
    --text-secondary: #d1d5db;
    --border-color: #4b5563;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.3);
}

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

html, body {
    width: 100%;
    height: 100%;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Microsoft YaHei', sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    transition: background-color 0.3s, color 0.3s;
    line-height: 1.6;
}

/* 應用容器 */
.app-container {
    width: 100%;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* 頁面切換 */
.screen {
    display: none;
    width: 100%;
    flex: 1;
    animation: fadeIn 0.3s ease-in;
}

.screen.active {
    display: flex;
    flex-direction: column;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

/* 頂部欄 */
.header, .game-header {
    background-color: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem;
    box-shadow: var(--shadow);
}

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

.header-content {
    text-align: center;
    flex: 1;
}

.title {
    font-size: 2rem;
    font-weight: 700;
    letter-spacing: 0.1em;
    margin-bottom: 0.25rem;
}

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

/* 遊戲頂部欄 */
.game-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.75rem 1rem;
}

.game-header-left, .game-header-center, .game-header-right {
    flex: 1;
    display: flex;
    justify-content: center;
    align-items: center;
}

.game-header-left {
    justify-content: flex-start;
}

.game-header-right {
    justify-content: flex-end;
}

.difficulty-display {
    font-size: 1rem;
    font-weight: 600;
}

.timer {
    font-size: 1.5rem;
    font-weight: 700;
    font-family: 'Courier New', monospace;
    min-width: 80px;
    text-align: center;
}

/* 主題切換按鈕 */
.theme-toggle {
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    padding: 0.5rem;
    border-radius: 0.5rem;
    transition: background-color 0.2s;
    display: flex;
    align-items: center;
    justify-content: center;
}

.theme-toggle:hover {
    background-color: var(--bg-tertiary);
}

.theme-icon {
    display: inline-block;
}

/* 首頁內容 */
.home-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 2rem 1rem;
    gap: 3rem;
}

.difficulty-section,
.info-section {
    width: 100%;
    max-width: 600px;
}

.difficulty-section h2,
.info-section h3 {
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
    text-align: center;
}

.difficulty-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 1rem;
}

.difficulty-btn {
    padding: 1.5rem 1rem;
    background-color: var(--bg-secondary);
    border: 2px solid var(--border-color);
    border-radius: 0.75rem;
    cursor: pointer;
    transition: all 0.2s;
    font-size: 1rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.5rem;
    color: var(--text-primary);
}

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

.difficulty-level {
    font-weight: 700;
    font-size: 1.25rem;
}

.difficulty-label {
    font-size: 0.75rem;
    opacity: 0.7;
}

.info-card {
    background-color: var(--bg-secondary);
    padding: 1.5rem;
    border-radius: 0.75rem;
    border-left: 4px solid var(--primary-color);
}

.info-card h3 {
    margin-bottom: 1rem;
    font-size: 1.125rem;
    text-align: left;
}

.info-card ul {
    list-style: none;
    padding-left: 0;
}

.info-card li {
    padding: 0.5rem 0;
    padding-left: 1.5rem;
    position: relative;
    color: var(--text-secondary);
}

.info-card li:before {
    content: "✓";
    position: absolute;
    left: 0;
    color: var(--success-color);
    font-weight: 700;
}

/* 底部 */
.footer {
    text-align: center;
    padding: 1.5rem;
    color: var(--text-secondary);
    border-top: 1px solid var(--border-color);
    font-size: 0.875rem;
}

/* 按鈕通用樣式 */
button {
    font-family: inherit;
    font-size: inherit;
}

/* 響應式設計 */
@media (max-width: 768px) {
    .title {
        font-size: 1.5rem;
    }
    
    .difficulty-buttons {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .home-content {
        padding: 1rem;
        gap: 1.5rem;
    }
}

@media (max-width: 480px) {
    .title {
        font-size: 1.25rem;
    }
    
    .difficulty-buttons {
        grid-template-columns: 1fr;
    }
    
    .difficulty-btn {
        padding: 1rem;
    }
}

/* 隱藏元素 */
.hidden {
    display: none !important;
}