:root {
    --primary-color: #0066cc;
    --secondary-color: #6366f1;
    --success-color: #10b981;
    --background: #ffffff;
    --surface: #f8fafc;
    --border: #e2e8f0;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --radius: 12px;
    --transition: all 0.2s ease;
}

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

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

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

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

h1 {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 10px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.subtitle {
    font-size: 1.125rem;
    color: var(--text-secondary);
    margin-bottom: 20px;
}

.language-selector {
    position: absolute;
    top: 0;
    right: 0;
}

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

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

.converter-section {
    background: var(--background);
    border-radius: var(--radius);
    padding: 30px;
    box-shadow: var(--shadow-md);
    margin-bottom: 40px;
}

.input-group {
    margin-bottom: 30px;
}

.input-group label {
    display: block;
    font-weight: 600;
    margin-bottom: 10px;
    color: var(--text-primary);
}

.input-wrapper {
    display: flex;
    gap: 10px;
}

.input-wrapper input[type="number"] {
    flex: 1;
    padding: 12px 16px;
    font-size: 18px;
    border: 2px solid var(--border);
    border-radius: 8px;
    transition: var(--transition);
}

.input-wrapper input[type="number"]:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(0, 102, 204, 0.1);
}

.input-wrapper select {
    padding: 12px 16px;
    font-size: 18px;
    border: 2px solid var(--border);
    border-radius: 8px;
    background-color: var(--background);
    cursor: pointer;
    transition: var(--transition);
}

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

.settings-group {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
    margin-bottom: 30px;
    padding: 20px;
    background-color: var(--surface);
    border-radius: 8px;
}

.setting-item label {
    display: block;
    font-size: 14px;
    font-weight: 500;
    margin-bottom: 5px;
    color: var(--text-secondary);
}

.setting-item input {
    width: 100%;
    padding: 8px 12px;
    border: 1px solid var(--border);
    border-radius: 6px;
    font-size: 14px;
    transition: var(--transition);
}

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

.results-section h2 {
    font-size: 1.5rem;
    margin-bottom: 20px;
    color: var(--text-primary);
}

.results-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(120px, 1fr));
    gap: 15px;
}

.result-item {
    background: var(--surface);
    padding: 15px;
    border-radius: 8px;
    text-align: center;
    cursor: pointer;
    transition: var(--transition);
    position: relative;
    border: 1px solid var(--border);
}

.result-item:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
    border-color: var(--primary-color);
}

.result-value {
    display: block;
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--primary-color);
    margin-bottom: 5px;
}

.result-unit {
    display: block;
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.copy-notification {
    position: absolute;
    top: -30px;
    left: 50%;
    transform: translateX(-50%);
    background: var(--success-color);
    color: white;
    padding: 4px 12px;
    border-radius: 4px;
    font-size: 12px;
    animation: fadeInOut 2s ease;
}

@keyframes fadeInOut {
    0% { opacity: 0; transform: translateX(-50%) translateY(10px); }
    20% { opacity: 1; transform: translateX(-50%) translateY(0); }
    80% { opacity: 1; transform: translateX(-50%) translateY(0); }
    100% { opacity: 0; transform: translateX(-50%) translateY(-10px); }
}

.common-values {
    margin-top: 30px;
}

.common-values h3 {
    font-size: 1.125rem;
    margin-bottom: 15px;
    color: var(--text-primary);
}

.preset-buttons {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.preset-btn {
    padding: 8px 16px;
    border: 1px solid var(--border);
    border-radius: 6px;
    background: var(--background);
    color: var(--text-primary);
    font-size: 14px;
    cursor: pointer;
    transition: var(--transition);
}

.preset-btn:hover {
    background: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}

.info-section {
    margin-top: 60px;
}

.info-section h2 {
    font-size: 1.875rem;
    margin-bottom: 30px;
    text-align: center;
    color: var(--text-primary);
}

.info-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 20px;
}

.info-card {
    background: var(--background);
    padding: 25px;
    border-radius: var(--radius);
    box-shadow: var(--shadow-sm);
    transition: var(--transition);
}

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

.info-card h3 {
    font-size: 1.25rem;
    margin-bottom: 10px;
    color: var(--primary-color);
}

.info-card p {
    color: var(--text-secondary);
    line-height: 1.6;
}

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

/* レスポンシブ対応 */
@media (max-width: 768px) {
    .container {
        padding: 15px;
    }
    
    h1 {
        font-size: 2rem;
    }
    
    .subtitle {
        font-size: 1rem;
    }
    
    .converter-section {
        padding: 20px;
    }
    
    .input-wrapper {
        flex-direction: column;
    }
    
    .input-wrapper input[type="number"],
    .input-wrapper select {
        width: 100%;
    }
    
    .results-grid {
        grid-template-columns: repeat(auto-fill, minmax(100px, 1fr));
    }
    
    .language-selector {
        position: static;
        margin-top: 15px;
    }
}

/* ダークモード対応（システム設定に応じて） */
@media (prefers-color-scheme: dark) {
    :root {
        --background: #0f172a;
        --surface: #1e293b;
        --border: #334155;
        --text-primary: #f1f5f9;
        --text-secondary: #94a3b8;
    }
    
    .language-selector select,
    .input-wrapper input[type="number"],
    .input-wrapper select,
    .setting-item input {
        background-color: var(--surface);
        color: var(--text-primary);
    }
    
    .preset-btn {
        background: var(--surface);
        color: var(--text-primary);
    }
    
    .preset-btn:hover {
        background: var(--primary-color);
        color: white;
    }
}