/* 首屏关键样式（内嵌或优先加载） */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: system-ui;
    background: linear-gradient(135deg, #f5f7fa 0%, #e9eef3 100%);
    padding: 2rem 1rem;
}

.card {
    background: rgba(255, 255, 255, 0.95);
    max-width: 550px;
    margin: 0 auto;
    padding: 2rem 1.8rem;
    border-radius: 32px;
}

.nav {
    text-align: center;
    margin-bottom: 2rem;
}

.nav a {
    display: inline-block;
    margin: 0 0.75rem;
    color: #2563eb;
    text-decoration: none;
}