<style>
    .my-flex-table {
      display: flex;
      display: -webkit-flex;
      flex-wrap: wrap;
      -webkit-flex-wrap: wrap;
      width: 100%;
    }

    .my-flex-cell {
      width: 33.333%;
      border: 1px solid #ddd;
      box-sizing: border-box;
      padding: 5px;
    }

    .my-flex-cell-content img {
      width: 100%!important;
      height: auto!important;
    }
</style>

<div class="my-flex-table">
    <div class="my-flex-cell">
        <div class="my-flex-cell-content">
            INHALTE HIER
        </div>
    </div>
    <div class="my-flex-cell">
        <div class="my-flex-cell-content">
            INHALTE HIER
        </div>
    </div>
    <div class="my-flex-cell">
        <div class="my-flex-cell-content">
            INHALTE HIER
        </div>
    </div>
  </div>
</div>