SOURCE

<div class="wrap">
<div class="row">
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
</div>
  
<div class="row">
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
</div>
  
<div class="row">
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
</div>
</div>

*{
  margin:0;
  padding:0;
}
.wrap {
  min-width: 480px;
}
.box {
  --box-width:30vw;
  width: var(--box-width);
  height:var(--box-width);
  /*background-color:#fea500;*/
  border: 1px solid gray;
  float:left;
  border-radius:8px;
  margin:5px;
  min-width: 120px;
}