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

body {
    min-height: 100vh;      /* 改为 min-height，内容多时自动扩展 */
    font-family: 'Segoe UI', system-ui, sans-serif;
    display: flex;
    flex-direction: column; /* 纵向排列 */
    justify-content: center;
    align-items: center;
}