<style>
.el {
  width: 150px;
  height: 150px;
  background-color: green;
}
</style>

<div class="el el1">
</div>

<div class="el el2" >
</div>

<div class="el el3" style="position: relative;">
<div style="background: red; width: 10px; height: 10px; position: absolute; top: 0; left: 0;"></div>
</div>