:root {
            --primary: #6366f1;
            --primary-dark: #4f46e5;
            --bg: #f8fafc;
            --card-bg: #ffffff;
            --text: #1e293b;
            --text-secondary: #64748b;
            --border: #e2e8f0;
            --success: #22c55e;
            --error: #ef4444;
            --warning: #f59e0b;
            --shadow: 0 1px 3px rgba(0,0,0,0.1), 0 1px 2px rgba(0,0,0,0.06);
            --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.1), 0 4px 6px -2px rgba(0,0,0,0.05);
        }

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

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

        /* Header */
        header {
            padding: 2.5rem 1rem 1.5rem;
            text-align: center;
        }

        header h1 {
            font-size: 1.8rem;
            font-weight: 700;
            margin-bottom: 0.75rem;
            line-height: 1.3;
        }

        header p {
            max-width: 640px;
            margin: 0 auto;
            opacity: 0.9;
            font-size: 1rem;
            line-height: 1.6;
            color: var(--text-secondary);
        }

        .container {
            max-width: 800px;
            margin: 0 auto;
            padding: 0 1.5rem 1.5rem;
        }

        /* Tool Card */
        .tool-card {
            background: var(--card-bg);
            border-radius: 16px;
            box-shadow: var(--shadow-lg);
            overflow: hidden;
            margin-bottom: 2rem;
        }

        .current-ts {
            padding: 1.5rem;
            background: linear-gradient(135deg, #f0f9ff 0%, #e0f2fe 100%);
            border-bottom: 1px solid var(--border);
            text-align: center;
        }

        .current-ts .label {
            font-size: 0.875rem;
            color: var(--text-secondary);
            margin-bottom: 0.5rem;
        }

        .current-ts .ts-value {
            font-family: 'SF Mono', Monaco, 'Cascadia Code', monospace;
            font-size: 1.5rem;
            font-weight: 700;
            color: var(--primary-dark);
            letter-spacing: 0.5px;
        }

        .current-ts .ts-date {
            font-size: 0.95rem;
            color: var(--text-secondary);
            margin-top: 0.25rem;
        }

        .converter {
            padding: 1.5rem;
        }

        .convert-block {
            padding: 1rem 0;
        }

        .convert-block:first-child {
            padding-top: 0;
        }

        .block-title {
            font-size: 1.1rem;
            font-weight: 600;
            color: var(--text);
            margin-bottom: 1rem;
        }

        .divider {
            height: 1px;
            background: var(--border);
            margin: 0.5rem 0;
        }

        .input-group {
            display: flex;
            gap: 0.75rem;
            flex-wrap: wrap;
            margin-bottom: 1rem;
        }

        .input-group input, .input-group select {
            flex: 1;
            min-width: 200px;
            padding: 0.875rem 1rem;
            border: 2px solid var(--border);
            border-radius: 10px;
            font-size: 1rem;
            transition: all 0.2s;
            outline: none;
            font-family: inherit;
            color: var(--text);
        }

        .input-group input:focus, .input-group select:focus {
            border-color: var(--primary);
            box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
        }

        .input-group input::placeholder {
            color: var(--text-secondary);
        }

        .btn {
            padding: 0.875rem 1.5rem;
            border: none;
            border-radius: 10px;
            font-size: 1rem;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.2s;
            display: inline-flex;
            align-items: center;
            gap: 0.5rem;
        }

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

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

        .btn-secondary {
            background: var(--bg);
            color: var(--text);
            border: 2px solid var(--border);
        }

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

        .result-area {
            background: #f8fafc;
            border-radius: 12px;
            padding: 1.25rem;
            margin-top: 1rem;
            border: 1px solid var(--border);
            display: none;
        }

        .result-area.active {
            display: block;
        }

        .result-area .result-label {
            font-size: 0.875rem;
            color: var(--text-secondary);
            margin-bottom: 0.5rem;
        }

        .result-area .result-value {
            font-family: 'SF Mono', Monaco, 'Cascadia Code', monospace;
            font-size: 1.25rem;
            font-weight: 600;
            color: var(--text);
            word-break: break-all;
        }

        .result-area .result-meta {
            font-size: 0.875rem;
            color: var(--text-secondary);
            margin-top: 0.5rem;
        }

        .copy-btn {
            margin-top: 0.75rem;
            padding: 0.4rem 1rem;
            background: white;
            border: 1px solid var(--border);
            border-radius: 8px;
            font-size: 0.875rem;
            color: var(--text);
            cursor: pointer;
            transition: all 0.2s;
        }

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

        .copy-btn.copied {
            background: var(--success);
            color: white;
            border-color: var(--success);
        }

        /* Content Cards - Single Column */
        .content-card {
            background: var(--card-bg);
            border-radius: 12px;
            padding: 1.5rem 2rem;
            box-shadow: var(--shadow);
            margin-bottom: 1.5rem;
        }

        .content-card h2 {
            font-size: 1.25rem;
            font-weight: 700;
            margin-bottom: 1rem;
            color: var(--text);
            padding-bottom: 0.5rem;
            border-bottom: 2px solid var(--primary);
            display: inline-block;
        }

        .content-card h3 {
            font-size: 1.1rem;
            font-weight: 600;
            margin: 1.5rem 0 0.75rem;
            color: var(--text);
        }

        .content-card p {
            color: var(--text-secondary);
            line-height: 1.9;
            margin-bottom: 1rem;
            font-size: 0.98rem;
        }

        .content-card ul, .content-card ol {
            padding-left: 1.5rem;
            margin: 1rem 0;
        }

        .content-card li {
            color: var(--text-secondary);
            line-height: 1.9;
            margin-bottom: 0.5rem;
            font-size: 0.98rem;
        }

        .content-card code {
            background: #f1f5f9;
            padding: 0.15rem 0.4rem;
            border-radius: 4px;
            font-size: 0.9rem;
            color: var(--primary-dark);
            font-family: 'SF Mono', Monaco, monospace;
        }

        .content-card strong {
            color: var(--text);
        }

        .content-card a {
            color: var(--primary);
            text-decoration: none;
        }

        .content-card a:hover {
            text-decoration: underline;
        }

        /* FAQ */
        .faq-item {
            border-bottom: 1px solid var(--border);
            padding: 1rem 0;
        }

        .faq-item:last-child {
            border-bottom: none;
        }

        .faq-question {
            font-size: 1rem;
            font-weight: 600;
            color: var(--text);
            margin-bottom: 0.5rem;
            cursor: pointer;
            display: flex;
            justify-content: space-between;
            align-items: center;
            list-style: none;
        }

        .faq-question::-webkit-details-marker {
            display: none;
        }

        .faq-answer {
            color: var(--text-secondary);
            font-size: 0.95rem;
            line-height: 1.8;
        }

        .faq-toggle {
            width: 24px;
            height: 24px;
            display: flex;
            align-items: center;
            justify-content: center;
            color: var(--text-secondary);
            transition: transform 0.2s;
            flex-shrink: 0;
        }

        details[open] .faq-toggle {
            transform: rotate(180deg);
        }

        /* Tip/Warning Boxes */
        .tip-box {
            background: #eff6ff;
            border-left: 4px solid var(--primary);
            padding: 1rem 1.25rem;
            border-radius: 0 8px 8px 0;
            margin: 1.25rem 0;
        }

        .tip-box p {
            margin: 0;
            color: #1e40af;
            font-size: 0.95rem;
        }

        .highlight-box {
            background: #f0fdf4;
            border-left: 4px solid var(--success);
            padding: 1rem 1.25rem;
            border-radius: 0 8px 8px 0;
            margin: 1.25rem 0;
        }

        .highlight-box p {
            margin: 0;
            color: #166534;
            font-size: 0.95rem;
        }

        /* Footer */
        footer {
            text-align: center;
            padding: 2rem 1rem;
            color: var(--text-secondary);
            font-size: 0.875rem;
            border-top: 1px solid var(--border);
            margin-top: 2rem;
        }

        footer a {
            color: var(--primary);
            text-decoration: none;
        }

        footer a:hover {
            text-decoration: underline;
        }

        footer .footer-links {
            margin-bottom: 0.75rem;
            display: flex;
            justify-content: center;
            flex-wrap: wrap;
            gap: 0.75rem;
        }

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

        footer .footer-links a:hover {
            color: var(--primary);
        }

        /* Toast */
        .toast {
            position: fixed;
            bottom: 2rem;
            left: 50%;
            transform: translateX(-50%) translateY(100px);
            background: #1e293b;
            color: white;
            padding: 0.875rem 1.5rem;
            border-radius: 10px;
            font-size: 0.875rem;
            z-index: 1000;
            opacity: 0;
            transition: all 0.3s ease;
            box-shadow: var(--shadow-lg);
        }

        .toast.show {
            transform: translateX(-50%) translateY(0);
            opacity: 1;
        }

        .toast.success {
            background: var(--success);
        }

        .toast.error {
            background: var(--error);
        }

        /* Responsive */
        @media (max-width: 640px) {
            header h1 {
                font-size: 1.4rem;
            }

            header p {
                font-size: 0.9rem;
            }

            .input-group {
                flex-direction: column;
            }

            .input-group input, .input-group select {
                min-width: 100%;
            }

            .btn {
                width: 100%;
                justify-content: center;
            }

            .container {
                padding: 0 1rem 1rem;
            }

            .current-ts .ts-value {
                font-size: 1.25rem;
            }

            .content-card {
                padding: 1.25rem;
            }
        }