:root {
            color-scheme: light;
            --background: #f5f7fb;
            --card: #ffffff;
            --text: #18212f;
            --muted: #6b7280;
            --line: #e5e7eb;
            --accent: #2563eb;
            --spinner-track: #dbe5f5;
            --shadow: 0 18px 50px rgba(15, 23, 42, 0.10);
        }

        @media (prefers-color-scheme: dark) {
            :root {
                color-scheme: dark;
                --background: #0f141c;
                --card: #171e29;
                --text: #f3f4f6;
                --muted: #9ca3af;
                --line: #2a3442;
                --accent: #60a5fa;
                --spinner-track: #2c3a4d;
                --shadow: 0 18px 50px rgba(0, 0, 0, 0.30);
            }
        }

        * {
            box-sizing: border-box;
        }

        html,
        body {
            min-height: 100%;
        }

        body {
            margin: 0;
            display: grid;
            place-items: center;
            padding: 24px;
            background: var(--background);
            color: var(--text);
            font-family:
                -apple-system,
                BlinkMacSystemFont,
                "Segoe UI",
                Roboto,
                Helvetica,
                Arial,
                sans-serif;
        }

        .card {
            width: 100%;
            max-width: 520px;
            padding: 40px 36px 28px;
            text-align: center;
            background: var(--card);
            border: 1px solid var(--line);
            border-radius: 18px;
            box-shadow: var(--shadow);
        }

        .spinner {
            width: 54px;
            height: 54px;
            margin: 0 auto 26px;
            border: 5px solid var(--spinner-track);
            border-top-color: var(--accent);
            border-radius: 50%;
            animation: spin 0.85s linear infinite;
        }

        h1 {
            margin: 0 0 12px;
            font-size: 25px;
            line-height: 1.25;
            letter-spacing: -0.02em;
        }

        .description {
            max-width: 410px;
            margin: 0 auto;
            color: var(--muted);
            font-size: 15px;
            line-height: 1.65;
        }

        .diagnostics {
            margin-top: 30px;
            padding-top: 20px;
            text-align: left;
            border-top: 1px solid var(--line);
        }

        .diagnostics-title {
            margin: 0 0 12px;
            color: var(--muted);
            font-size: 12px;
            font-weight: 600;
            letter-spacing: 0.08em;
            text-transform: uppercase;
        }

        .diagnostics-row {
            display: flex;
            justify-content: space-between;
            gap: 20px;
            padding: 6px 0;
            font-size: 13px;
            line-height: 1.4;
        }

        .diagnostics-label {
            flex: 0 0 auto;
            color: var(--muted);
        }

        .diagnostics-value {
            min-width: 0;
            overflow-wrap: anywhere;
            text-align: right;
            font-family:
                "SFMono-Regular",
                Consolas,
                "Liberation Mono",
                monospace;
        }

        .error {
            display: none;
            margin-top: 20px;
            padding: 12px 14px;
            color: #991b1b;
            background: #fef2f2;
            border: 1px solid #fecaca;
            border-radius: 10px;
            font-size: 13px;
            line-height: 1.5;
        }

        .error.is-visible {
            display: block;
        }

        @media (prefers-color-scheme: dark) {
            .error {
                color: #fecaca;
                background: #3f1d24;
                border-color: #7f1d1d;
            }
        }

        @media (max-width: 520px) {
            .card {
                padding: 34px 24px 24px;
                border-radius: 14px;
            }

            .diagnostics-row {
                display: block;
            }

            .diagnostics-value {
                margin-top: 3px;
                text-align: left;
            }
        }

        @media (prefers-reduced-motion: reduce) {
            .spinner {
                animation-duration: 1.8s;
            }
        }

        @keyframes spin {
            to {
                transform: rotate(360deg);
            }
        }