<div class="block blue"></div>
<div class="block yellow"></div>
<div class="block green"></div>
.block{
display:block;
width: 50px;
height: 50px;
}
.yellow{
background-color: yellow;
}
.green{
background-color: green;
}
.blue{
background-color: blue;
}
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This Pen doesn't use any external JavaScript resources.