Button format

by Jools Chadwick

HTML

<div>
<button class="explicitSize"></button>
</div>

<div>
<button><span></span></button>
</div>

CSS

html,body{ margin:0; padding:0; border:0;}

div{
  background-color:green;
  line-height:0px;
  border:1px solid black;
}
button{
  background-color:blue;
  border: none;
  padding:0px;
}
.explicitSize{
  height: 20px;
  width: 20px;
}
span{
  display:block;
  height:20px;
  width:20px;
}