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

:root {
    --primary-color: #0052CC;
    --primary-hover: #0747A6;
    --secondary-color: #42526E;
    --background: #FAFBFC;
    --surface: #FFFFFF;
    --border: #DFE1E6;
    --text-primary: #172B4D;
    --text-secondary: #6B778C;
    --success: #00875A;
    --error: #DE350B;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.08);
    --shadow-md: 0 2px 8px rgba(0, 0, 0, 0.12);
    --shadow-lg: 0 8px 16px rgba(0, 0, 0, 0.16);
    --radius: 8px;
    --radius-sm: 4px;
    --transition: all 0.2s ease;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Fira Sans', 'Droid Sans', 'Helvetica Neue', sans-serif;
    background-color: var(--background);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 24px;
}

header {
    text-align: center;
    margin-bottom: 48px;
    padding-top: 24px;
}

.title {
    font-size: 48px;
    font-weight: 700;
    color: var(--primary-color);
    letter-spacing: -1px;
    margin-bottom: 8px;
    background: linear-gradient(135deg, #0052CC 0%, #0747A6 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.subtitle {
    font-size: 20px;
    color: var(--text-secondary);
    font-weight: 400;
}

main {
    display: grid;
    gap: 32px;
}

.input-section,
.output-section {
    background: var(--surface);
    border-radius: var(--radius);
    padding: 24px;
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--border);
}

.label {
    display: block;
    font-size: 14px;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.textarea {
    width: 100%;
    padding: 16px;
    border: 2px solid var(--border);
    border-radius: var(--radius-sm);
    font-family: 'SF Mono', Monaco, 'Cascadia Code', 'Roboto Mono', Consolas, 'Courier New', monospace;
    font-size: 14px;
    line-height: 1.5;
    resize: vertical;
    transition: var(--transition);
    background-color: var(--background);
}

.textarea:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(0, 82, 204, 0.1);
}

.textarea:read-only {
    background-color: #F4F5F7;
    cursor: default;
}

.input-stats {
    margin-top: 8px;
    font-size: 12px;
    color: var(--text-secondary);
    text-align: right;
}

.transform-options {
    background: var(--surface);
    border-radius: var(--radius);
    padding: 32px;
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--border);
}

.section-title {
    font-size: 24px;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 24px;
}

.option-group {
    margin-bottom: 32px;
}

.option-group:last-child {
    margin-bottom: 0;
}

.group-title {
    font-size: 16px;
    font-weight: 600;
    color: var(--secondary-color);
    margin-bottom: 16px;
    padding-bottom: 8px;
    border-bottom: 1px solid var(--border);
}

.button-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 12px;
}

.transform-btn {
    padding: 12px 20px;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    background: var(--surface);
    color: var(--text-primary);
    font-size: 14px;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

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

.transform-btn:active,
.transform-btn.active {
    transform: translateY(0);
    background-color: var(--primary-color);
    color: white;
}

.output-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 8px;
}

.output-actions {
    display: flex;
    gap: 8px;
}

.action-btn {
    padding: 8px 16px;
    border: none;
    border-radius: var(--radius-sm);
    font-size: 14px;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
}

.action-btn:not(.secondary) {
    background-color: var(--primary-color);
    color: white;
}

.action-btn:not(.secondary):hover {
    background-color: var(--primary-hover);
    transform: translateY(-1px);
    box-shadow: var(--shadow-sm);
}

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

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

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

footer {
    margin-top: 64px;
    padding: 32px 0;
    text-align: center;
    border-top: 1px solid var(--border);
}

.language-selector {
    margin-bottom: 16px;
}

.language-select {
    padding: 8px 16px;
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    background-color: var(--surface);
    color: var(--text-primary);
    font-size: 14px;
    cursor: pointer;
    transition: var(--transition);
}

.language-select:hover {
    border-color: var(--primary-color);
}

.language-select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(0, 82, 204, 0.1);
}

.footer-text {
    font-size: 14px;
    color: var(--text-secondary);
}

/* レスポンシブデザイン */
@media (max-width: 768px) {
    .container {
        padding: 16px;
    }
    
    .title {
        font-size: 36px;
    }
    
    .subtitle {
        font-size: 16px;
    }
    
    .section-title {
        font-size: 20px;
    }
    
    .button-grid {
        grid-template-columns: 1fr;
    }
    
    .input-section,
    .output-section,
    .transform-options {
        padding: 16px;
    }
    
    .textarea {
        font-size: 16px;
    }
}

/* アニメーション */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.transform-btn,
.action-btn {
    animation: fadeIn 0.3s ease-out;
}

/* アクセシビリティ改善 */
@media (prefers-reduced-motion: reduce) {
    * {
        animation: none !important;
        transition: none !important;
    }
}

/* ダークモード対応 */
@media (prefers-color-scheme: dark) {
    :root {
        --primary-color: #579DFF;
        --primary-hover: #2684FF;
        --secondary-color: #8993A4;
        --background: #161A1D;
        --surface: #22272B;
        --border: #38414A;
        --text-primary: #C7D1DB;
        --text-secondary: #8C9BAB;
        --success: #1F845A;
        --error: #E34935;
    }
    
    .textarea {
        background-color: #1C2125;
    }
    
    .textarea:read-only {
        background-color: #2C333A;
    }
    
    .transform-btn {
        background: #2C333A;
        border-color: #38414A;
    }
    
    .transform-btn:hover {
        background-color: #38414A;
    }
}