CSS 现代布局实战：Flex 与 Grid

/* 三列自适应网格 */
.grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 16px;
}

/* Flex 水平垂直居中 */
.center {
  display: flex;
  align-items: center;
  justify-content: center;
}