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

:root {
    --primary-color: #0066cc;
    --primary-hover: #0052a3;
    --secondary-color: #6c757d;
    --success-color: #28a745;
    --error-color: #dc3545;
    --background: #f8f9fa;
    --surface: #ffffff;
    --text-primary: #212529;
    --text-secondary: #6c757d;
    --border-color: #dee2e6;
    --code-background: #f1f3f5;
    --shadow-sm: 0 2px 4px rgba(0,0,0,0.08);
    --shadow-md: 0 4px 6px rgba(0,0,0,0.1);
    --shadow-lg: 0 10px 15px rgba(0,0,0,0.1);
    --radius: 8px;
    --radius-lg: 12px;
}

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(--background);
    min-height: 100vh;
}

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

header {
    text-align: center;
    margin-bottom: 40px;
    padding: 40px 0 20px;
    position: relative;
}

h1 {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 10px;
    background: linear-gradient(135deg, #0066cc 0%, #0052a3 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.subtitle {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: 20px;
}

.language-selector {
    position: absolute;
    top: 20px;
    right: 20px;
}

#languageSelect {
    padding: 8px 16px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    background-color: var(--surface);
    font-size: 14px;
    cursor: pointer;
    transition: border-color 0.3s;
}

#languageSelect:hover {
    border-color: var(--primary-color);
}

.editor-container {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    gap: 20px;
    margin-bottom: 30px;
}

.editor-section {
    background: var(--surface);
    border-radius: var(--radius-lg);
    padding: 20px;
    box-shadow: var(--shadow-sm);
    transition: box-shadow 0.3s;
}

.editor-section:hover {
    box-shadow: var(--shadow-md);
}

.section-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 15px;
}

.section-header h2 {
    font-size: 1.2rem;
    font-weight: 600;
    color: var(--text-primary);
}

.code-editor {
    width: 100%;
    min-height: 300px;
    padding: 15px;
    border: 2px solid var(--border-color);
    border-radius: var(--radius);
    font-family: 'Monaco', 'Menlo', 'Ubuntu Mono', monospace;
    font-size: 14px;
    line-height: 1.5;
    background-color: var(--code-background);
    resize: vertical;
    transition: border-color 0.3s;
}

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

.convert-section {
    display: flex;
    align-items: center;
    justify-content: center;
}

.primary-btn, .secondary-btn {
    padding: 10px 24px;
    border: none;
    border-radius: var(--radius);
    font-size: 16px;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s;
    display: inline-flex;
    align-items: center;
    gap: 8px;
}

.primary-btn {
    background-color: var(--primary-color);
    color: white;
    box-shadow: var(--shadow-sm);
}

.primary-btn:hover {
    background-color: var(--primary-hover);
    box-shadow: var(--shadow-md);
    transform: translateY(-1px);
}

.secondary-btn {
    background-color: var(--surface);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

.secondary-btn:hover {
    background-color: var(--code-background);
    border-color: var(--primary-color);
}

.btn-icon {
    font-size: 20px;
    font-weight: bold;
}

.error-message, .success-message {
    margin-top: 10px;
    padding: 8px 12px;
    border-radius: var(--radius);
    font-size: 14px;
    display: none;
}

.error-message {
    background-color: #f8d7da;
    color: var(--error-color);
    border: 1px solid #f5c6cb;
}

.success-message {
    background-color: #d4edda;
    color: var(--success-color);
    border: 1px solid #c3e6cb;
}

.options-container {
    background: var(--surface);
    border-radius: var(--radius-lg);
    padding: 25px;
    margin-bottom: 30px;
    box-shadow: var(--shadow-sm);
}

.options-container h3 {
    font-size: 1.2rem;
    font-weight: 600;
    margin-bottom: 20px;
    color: var(--text-primary);
}

.options-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 15px;
}

.option-item {
    display: flex;
    align-items: center;
    gap: 10px;
    cursor: pointer;
    padding: 8px;
    border-radius: var(--radius);
    transition: background-color 0.2s;
}

.option-item:hover {
    background-color: var(--code-background);
}

.option-item input[type="checkbox"] {
    width: 18px;
    height: 18px;
    cursor: pointer;
}

.features {
    background: linear-gradient(135deg, #f8f9fa 0%, #e9ecef 100%);
    border-radius: var(--radius-lg);
    padding: 30px;
    margin-bottom: 40px;
}

.features h3 {
    font-size: 1.3rem;
    font-weight: 600;
    margin-bottom: 20px;
    color: var(--text-primary);
}

.features-list {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 15px;
    list-style: none;
}

.features-list li {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 10px;
    background: var(--surface);
    border-radius: var(--radius);
    box-shadow: var(--shadow-sm);
}

.features-list li::before {
    content: "✓";
    color: var(--success-color);
    font-weight: bold;
    font-size: 18px;
}

footer {
    text-align: center;
    padding: 30px 0;
    color: var(--text-secondary);
    font-size: 14px;
    border-top: 1px solid var(--border-color);
    margin-top: 60px;
}

/* レスポンシブデザイン */
@media (max-width: 768px) {
    .container {
        padding: 15px;
    }
    
    header {
        padding: 20px 0 15px;
    }
    
    h1 {
        font-size: 2rem;
    }
    
    .language-selector {
        position: static;
        margin-top: 15px;
    }
    
    .editor-container {
        grid-template-columns: 1fr;
        gap: 15px;
    }
    
    .convert-section {
        order: -1;
        margin-bottom: 10px;
    }
    
    .primary-btn {
        width: 100%;
        justify-content: center;
    }
    
    .code-editor {
        min-height: 200px;
    }
    
    .options-grid {
        grid-template-columns: 1fr;
    }
    
    .features-list {
        grid-template-columns: 1fr;
    }
}

/* ダークモード対応 */
@media (prefers-color-scheme: dark) {
    :root {
        --background: #1a1a1a;
        --surface: #2d2d2d;
        --text-primary: #e0e0e0;
        --text-secondary: #a0a0a0;
        --border-color: #404040;
        --code-background: #252525;
    }
    
    .editor-section:hover {
        box-shadow: 0 4px 6px rgba(0,0,0,0.3);
    }
    
    .features {
        background: linear-gradient(135deg, #2d2d2d 0%, #252525 100%);
    }
}