:root {
            --bt74-bg: #0a0b10;
            --bt74-text: #e8eaed;
            --bt74-accent: #8ab4f8;
            --bt74-glass: rgba(255, 255, 255, 0.05);
            --bt74-glass-border: rgba(255, 255, 255, 0.1);
            --bt74-primary: #4285f4;
            --bt74-spacing-unit: 8px;
        }

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

        body {
            font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
            background-color: var(--bt74-bg);
            color: var(--bt74-text);
            line-height: 1.6;
            overflow-x: hidden;
            word-break: keep-all;
        }

        /* 导航栏设计 - 浮动毛玻璃 */
        .bt74-header {
            position: fixed;
            top: 24px;
            left: 50%;
            transform: translateX(-50%);
            width: 95%;
            max-width: 1400px;
            z-index: 1000;
            display: flex;
            flex-wrap: wrap;
            justify-content: space-between;
            align-items: center;
            padding: 12px 24px;
            background: rgba(10, 11, 16, 0.8);
            backdrop-filter: blur(20px);
            border: 1px solid var(--bt74-glass-border);
            border-radius: 50px;
            transition: all 0.4s ease;
        }

        .bt74-logo {
            flex: 0 0 auto;
            min-width: 0;
            display: flex;
            align-items: center;
        }

        .bt74-logo img {
            height: 32px;
            width: auto;
        }

        .bt74-nav {
            display: flex;
            flex-wrap: wrap;
            gap: 16px;
            list-style: none;
        }

        .bt74-nav-item {
            min-width: 0;
        }

        .bt74-nav-link {
            text-decoration: none;
            color: var(--bt74-text);
            font-size: 14px;
            font-weight: 500;
            padding: 8px 12px;
            border-radius: 20px;
            transition: background 0.3s ease;
            white-space: nowrap;
        }

        .bt74-nav-link:hover {
            background: var(--bt74-glass);
            color: var(--bt74-accent);
        }

        .bt74-nav-link.active {
            background: var(--bt74-primary);
            color: #fff;
        }

        /* Hero 区 - 非线性布局 */
        .bt74-hero {
            position: relative;
            min-height: 100vh;
            padding: 160px 5% 80px;
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            justify-content: center;
            overflow: hidden;
        }

        .bt74-hero-content {
            flex: 1;
            min-width: 320px;
            max-width: 700px;
            z-index: 2;
            word-break: break-word;
        }

        .bt74-hero-title {
            font-size: clamp(2.5rem, 5vw + 1rem, 4.5rem);
            line-height: 1.1;
            margin-bottom: 24px;
            font-weight: 800;
            background: linear-gradient(135deg, #fff 0%, var(--bt74-accent) 100%);
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
        }

        .bt74-hero-subtitle {
            font-size: clamp(1rem, 1.5vw + 0.5rem, 1.25rem);
            color: rgba(232, 234, 237, 0.7);
            margin-bottom: 40px;
            max-width: 600px;
        }

        .bt74-hero-visual {
            flex: 1;
            min-width: 320px;
            display: flex;
            justify-content: center;
            align-items: center;
            position: relative;
        }

        .bt74-parallax-card {
            width: 80%;
            aspect-ratio: 16/10;
            background: var(--bt74-glass);
            border: 1px solid var(--bt74-glass-border);
            border-radius: 24px;
            backdrop-filter: blur(10px);
            transform: perspective(1000px) rotateY(-15deg) rotateX(10deg);
            box-shadow: 0 50px 100px rgba(0,0,0,0.5);
            display: flex;
            flex-direction: column;
            padding: 24px;
        }

        /* 功能模块 - 呼吸感卡片 */
        .bt74-section {
            padding: 96px 5%;
            max-width: 1400px;
            margin: 0 auto;
        }

        .bt74-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
            gap: 32px;
            margin-top: 64px;
        }

        .bt74-card {
            background: var(--bt74-glass);
            border: 1px solid var(--bt74-glass-border);
            border-radius: 20px;
            padding: 40px;
            transition: transform 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275), background 0.3s;
            word-break: break-word;
        }

        .bt74-card:hover {
            transform: translateY(-10px);
            background: rgba(255, 255, 255, 0.08);
            border-color: var(--bt74-accent);
        }

        .bt74-card-tag {
            display: inline-block;
            padding: 4px 12px;
            background: rgba(138, 180, 248, 0.1);
            color: var(--bt74-accent);
            border-radius: 12px;
            font-size: 12px;
            margin-bottom: 16px;
            text-transform: uppercase;
        }

        .bt74-card h3 {
            font-size: 24px;
            margin-bottom: 16px;
            color: #fff;
        }

        /* 深度安全展示区 */
        .bt74-security-showcase {
            display: flex;
            flex-wrap: wrap;
            gap: 48px;
            align-items: center;
            margin-top: 80px;
        }

        .bt74-security-img-wrapper {
            flex: 1;
            min-width: 300px;
            position: relative;
        }

        .bt74-security-img {
            width: 100%;
            height: auto;
            border-radius: 24px;
            box-shadow: 0 20px 60px rgba(0,0,0,0.4);
            border: 1px solid var(--bt74-glass-border);
        }

        .bt74-security-text {
            flex: 1;
            min-width: 300px;
            word-break: break-word;
        }

        .bt74-btn {
            display: inline-block;
            padding: 16px 32px;
            background: var(--bt74-primary);
            color: #fff;
            text-decoration: none;
            border-radius: 30px;
            font-weight: 600;
            transition: all 0.3s;
            border: none;
            cursor: pointer;
            margin-top: 24px;
        }

        .bt74-btn:hover {
            box-shadow: 0 0 20px rgba(66, 133, 244, 0.5);
            transform: scale(1.05);
        }

        /* 页脚品牌区 */
        .bt74-footer {
            padding: 80px 5%;
            background: #050608;
            border-top: 1px solid var(--bt74-glass-border);
            text-align: center;
        }

        .bt74-footer-brand {
            font-size: 24px;
            font-weight: 700;
            margin-bottom: 24px;
            letter-spacing: -0.5px;
        }

        .bt74-footer-links {
            display: flex;
            flex-wrap: wrap;
            justify-content: center;
            gap: 32px;
            margin-bottom: 40px;
        }

        .bt74-footer-link {
            color: rgba(232, 234, 237, 0.5);
            text-decoration: none;
            font-size: 14px;
            transition: color 0.3s;
        }

        .bt74-footer-link:hover {
            color: var(--bt74-accent);
        }

        .bt74-copyright {
            font-size: 12px;
            color: rgba(232, 234, 237, 0.3);
        }

        /* 响应式调整 */
        @media (max-width: 768px) {
            .bt74-header {
                top: 0;
                width: 100%;
                border-radius: 0;
                padding: 10px 16px;
            }
            .bt74-nav {
                display: none; /* 简化移动端处理 */
            }
            .bt74-hero {
                padding-top: 120px;
                text-align: center;
            }
            .bt74-hero-visual {
                display: none;
            }
            .bt74-grid {
                grid-template-columns: 1fr;
            }
        }