* {
    box-sizing: border-box;
}

body {
    margin: 0;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background-color: #f8f9fa;
    min-height: 100vh;
    display: flex;
    flex-direction: column; /* 让 header 在上，main 在下 */
}
.main-content {
    flex: 1;
    display: flex;
    flex-direction: column;
}