To center a flexbox grid, you can use the `justify-content` and `align-items` properties. The `justify-content` property determines the horizontal alignment of items within a flex container, and the `align-items` property determines the vertical alignment of items within a flex container. To center items horizontally and vertically within a flex container, you can use the following CSS:
“`
.container {
display: flex;
justify-content: center;
align-items: center;
}
“`
This will align the items within the flex container so that they are centered both horizontally and vertically. You can also use the `align-content` property to center items within a flex container that have multiple rows or columns.