.cont {
            display: flex;
            flex-direction: row;
            justify-content: space-between;
            flex-wrap: wrap;
        }
 .cont > div {
            width: 30%;
        }

<div class="cont ">
        <div>item</div>
        <div>item</div>
        <div>item</div>
        <div>item</div>
        <div>item</div>
        <div>item</div>
        <div>item</div>
        <div>item</div>
        <div>item</div>
    </div>