<div class="row">
    <div class="col-xs">
        <div class="box">1</div>
    </div>
    <div class="col-xs">
        <div class="box">2</div>
    </div>
    <div class="col-xs">
        <div class="box">3</div>
    </div><div class="col-xs">
        <div class="box">4</div>
    </div>
</div>

.row {
  display: flex;
  flex-direction: row;
}

.box {
  min-width: 40px;
}