/* 基础变量与重置 */
        :root {
            --bt74-primary: #4285F4;
            --bt74-red: #EA4335;
            --bt74-yellow: #FBBC05;
            --bt74-green: #34A853;
            --bt74-dark: #202124;
            --bt74-light: #F8F9FA;
            --bt74-glass: rgba(255, 255, 255, 0.8);
            --bt74-spacing-unit: 8px;
            --bt74-container-width: 90vw;
            --bt74-max-content: 1400px;
        }

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

        body {
            font-family: 'Segoe UI', Roboto, 'Helvetica Neue', Arial, 'PingFang SC', 'Microsoft YaHei', sans-serif;
            background-color: var(--bt74-light);
            color: var(--bt74-dark);
            line-height: 1.6;
            overflow-x: hidden;
            word-break: break-word;
        }

        /* 流体字体 */
        h1 { font-size: clamp(2.5rem, 5vw + 1rem, 4.5rem); line-height: 1.1; font-weight: 800; white-space: normal; }
        h2 { font-size: clamp(1.8rem, 3vw + 0.5rem, 3rem); line-height: 1.2; font-weight: 700; white-space: normal; }
        h3 { font-size: clamp(1.2rem, 2vw + 0.5rem, 1.8rem); line-height: 1.3; font-weight: 600; white-space: normal; }
        p { font-size: clamp(1rem, 1vw + 0.5rem, 1.15rem); line-height: 1.8; color: #5f6368; }

        /* 布局组件 */
        .bt74-container {
            width: var(--bt74-container-width);
            max-width: var(--bt74-max-content);
            margin: 0 auto;
            padding: 0 calc(var(--bt74-spacing-unit) * 2);
        }

        .bt74-flex {
            display: flex;
            flex-wrap: wrap;
        }

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

        /* 导航栏 */
        .bt74-header {
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            z-index: 1000;
            background: var(--bt74-glass);
            backdrop-filter: blur(15px);
            border-bottom: 1px solid rgba(0,0,0,0.05);
            padding: calc(var(--bt74-spacing-unit) * 2) 0;
            transition: all 0.3s ease;
        }

        .bt74-nav-container {
            display: flex;
            justify-content: space-between;
            align-items: center;
            flex-wrap: wrap;
        }

        .bt74-logo {
            flex: 0 0 auto;
            min-width: 0;
        }

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

        .bt74-nav-list {
            display: flex;
            flex-wrap: wrap;
            list-style: none;
            gap: calc(var(--bt74-spacing-unit) * 3);
            margin-left: auto;
        }

        .bt74-nav-link {
            text-decoration: none;
            color: var(--bt74-dark);
            font-weight: 500;
            font-size: 0.95rem;
            padding: calc(var(--bt74-spacing-unit) * 1) calc(var(--bt74-spacing-unit) * 2);
            border-radius: 20px;
            transition: all 0.2s ease;
        }

        .bt74-nav-link:hover {
            background: rgba(66, 133, 244, 0.1);
            color: var(--bt74-primary);
        }

        .bt74-nav-active {
            background: var(--bt74-primary);
            color: white !important;
        }

        /* Hero 区块 - 独特堆叠布局 */
        .bt74-hero {
            padding: 160px 0 100px;
            background: radial-gradient(circle at 80% 20%, rgba(66, 133, 244, 0.08) 0%, transparent 40%),
                        radial-gradient(circle at 20% 80%, rgba(52, 168, 83, 0.08) 0%, transparent 40%);
            text-align: center;
            position: relative;
            overflow: hidden;
        }

        .bt74-hero-content {
            max-width: 900px;
            margin: 0 auto;
            position: relative;
            z-index: 2;
        }

        .bt74-hero-subtitle {
            margin-top: calc(var(--bt74-spacing-unit) * 3);
            margin-bottom: calc(var(--bt74-spacing-unit) * 5);
        }

        .bt74-hero-visual {
            margin-top: calc(var(--bt74-spacing-unit) * 8);
            position: relative;
            height: 400px;
            display: flex;
            justify-content: center;
            align-items: center;
        }

        /* 模拟标签页的流体组件 */
        .bt74-tab-card {
            background: white;
            padding: 20px;
            border-radius: 16px;
            box-shadow: 0 20px 40px rgba(0,0,0,0.08);
            position: absolute;
            width: 280px;
            transition: transform 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
            border: 1px solid rgba(0,0,0,0.03);
        }

        .bt74-tab-card:hover {
            transform: translateY(-15px) scale(1.05) !important;
            z-index: 10;
        }

        .bt74-card-1 { transform: rotate(-10deg) translateX(-150px); border-top: 4px solid var(--bt74-primary); }
        .bt74-card-2 { transform: rotate(5deg) translateY(-40px); border-top: 4px solid var(--bt74-red); z-index: 3; }
        .bt74-card-3 { transform: rotate(15deg) translateX(180px); border-top: 4px solid var(--bt74-green); }

        .bt74-card-header {
            display: flex;
            align-items: center;
            gap: 10px;
            margin-bottom: 12px;
        }

        .bt74-card-dot { width: 12px; height: 12px; border-radius: 50%; }
        .bt74-card-line { height: 8px; background: #eee; border-radius: 4px; flex-grow: 1; }

        /* 功能模块区块 */
        .bt74-section {
            padding: 96px 0;
        }

        .bt74-feature-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
            gap: calc(var(--bt74-spacing-unit) * 4);
        }

        .bt74-feature-card {
            background: white;
            padding: calc(var(--bt74-spacing-unit) * 6);
            border-radius: 24px;
            transition: all 0.3s ease;
            display: flex;
            flex-direction: column;
            height: 100%;
            border: 1px solid transparent;
        }

        .bt74-feature-card:hover {
            border-color: rgba(66, 133, 244, 0.2);
            box-shadow: 0 30px 60px rgba(0,0,0,0.05);
            transform: translateY(-8px);
        }

        .bt74-feature-icon {
            width: 64px;
            height: 64px;
            border-radius: 16px;
            display: flex;
            align-items: center;
            justify-content: center;
            margin-bottom: 24px;
            font-size: 2rem;
        }

        .bt74-bg-blue { background: rgba(66, 133, 244, 0.1); color: var(--bt74-primary); }
        .bt74-bg-red { background: rgba(234, 67, 53, 0.1); color: var(--bt74-red); }
        .bt74-bg-green { background: rgba(52, 168, 83, 0.1); color: var(--bt74-green); }

        .bt74-tag {
            display: inline-block;
            padding: 4px 12px;
            background: #f1f3f4;
            border-radius: 100px;
            font-size: 0.85rem;
            color: #5f6368;
            margin-top: 16px;
        }

        /* 响应式调整 */
        @media (max-width: 768px) {
            .bt74-nav-list {
                justify-content: center;
                gap: calc(var(--bt74-spacing-unit) * 1);
                margin: calc(var(--bt74-spacing-unit) * 2) auto 0;
            }
            .bt74-hero-visual {
                height: auto;
                flex-direction: column;
                gap: 20px;
            }
            .bt74-tab-card {
                position: static;
                width: 100%;
                transform: none !important;
            }
            .bt74-header {
                padding: var(--bt74-spacing-unit) 0;
            }
        }

        /* 页脚 */
        .bt74-footer {
            background: #fff;
            padding: 64px 0;
            border-top: 1px solid #eee;
            text-align: center;
        }

        .bt74-footer-brand {
            font-size: 1.5rem;
            font-weight: 700;
            color: var(--bt74-dark);
            margin-bottom: 16px;
        }

        .bt74-footer-links {
            display: flex;
            justify-content: center;
            gap: 24px;
            margin-bottom: 32px;
            flex-wrap: wrap;
        }

        .bt74-footer-links a {
            color: #5f6368;
            text-decoration: none;
            font-size: 0.9rem;
            transition: color 0.2s;
        }

        .bt74-footer-links a:hover { color: var(--bt74-primary); }

        .bt74-copyright {
            color: #9aa0a6;
            font-size: 0.85rem;
        }

        /* 按钮设计 */
        .bt74-btn {
            display: inline-block;
            padding: 16px 32px;
            border-radius: 100px;
            font-weight: 600;
            text-decoration: none;
            transition: all 0.3s ease;
            cursor: pointer;
            border: none;
        }

        .bt74-btn-primary {
            background: var(--bt74-primary);
            color: white;
            box-shadow: 0 4px 15px rgba(66, 133, 244, 0.3);
        }

        .bt74-btn-primary:hover {
            background: #3367d6;
            transform: scale(1.05);
            box-shadow: 0 6px 20px rgba(66, 133, 244, 0.4);
        }