/* 基础重置和暗黑背景 */
    *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
    body { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif; background: #0b0f1a; color: #e5e7eb; line-height: 1.6; -webkit-font-smoothing: antialiased; }
    a { color: inherit; text-decoration: none; }
    ul { list-style: none; }

    /* 顶部导航 */
    .top-nav {
        position: sticky; top: 0; z-index: 100;
        background: rgba(11,15,26,0.85); backdrop-filter: blur(12px);
        border-bottom: 1px solid #1f2937;
        padding: 0 40px; height: 56px;
        display: flex; align-items: center; justify-content: space-between;
    }
    .top-nav .brand { font-size: 18px; font-weight: 700; letter-spacing: -0.5px; }
    .top-nav .brand span { background: linear-gradient(135deg, #6366f1, #7c3aed); -webkit-background-clip: text; -webkit-text-fill-color: transparent; }
    .top-nav .nav-links { display: flex; gap: 28px; font-size: 14px; color: #9ca3af; }
    .top-nav .nav-links a:hover { color: #e5e7eb; }
    .top-nav .nav-right { display: flex; gap: 16px; font-size: 14px; align-items: center; }
    .top-nav .nav-right a.btn-login { color: #9ca3af; }
    .top-nav .nav-right a.btn-signup { background: linear-gradient(135deg, #6366f1, #7c3aed); color: #fff; padding: 6px 18px; border-radius: 6px; font-weight: 500; }