html code checker online code example

Example: html checker

<style>
#checker{
  display:flex;
  flex-direction:column;
}

.row{
  display:flex;
}
.row div{
  width:50px;
  height:50px;
  border:solid;
  border-width:1px;
}

.row1 div:nth-child(odd){
  background-color:black;
}

.row2 div:nth-child(even){
  background-color:black;
}
</style>

<div id='checker'>
  <div class='row row1'> 
     <div></div>
     <div></div>
     <div></div>
     <div></div>
     <div></div>
  </div>
    <div class='row row2'> 
     <div></div>
     <div></div>
     <div></div>
     <div></div>
     <div></div>
  </div>
     <div class='row row1'> 
     <div></div>
     <div></div>
     <div></div>
     <div></div>
     <div></div>
  </div>
  <div class='row row2'> 
     <div></div>
     <div></div>
     <div></div>
     <div></div>
     <div></div>
  </div>
    <div class='row row1'> 
     <div></div>
     <div></div>
     <div></div>
     <div></div>
     <div></div>
  </div>
</div>