How to implement the nine-square grid style in Flex layout in css (code)

nbsp;html>

<style>
.block {
    padding-top: 30%;
    margin-top: 3%;
    border-radius: 10%;
    background-color: orange;
    width: 30%;
}
.container-flex2  {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-around;
}
</style>

   <div>
        <div></div>
        <div></div>
        <div></div>
        <div></div>
        <div></div>
        <div></div>
        <div></div>
        <div></div>
        <div></div>
    </div>