<style>
div {
  width: 50px;
  height: 50px;
}
</style>
<div style="background-color: blue"></div>
<div style="background-color: green"></div>
<div></div>
<div style="background-color: green"></div>
<div style="background-color: blue"></div>
<div></div>
<div style="background-color: green"></div>
