JSFiddle - React, Tailwind, and code Playground

HTML

<div class="checker">
</div>
<div class="red boxes">
</div>
<div class="green boxes">
</div>
<div class="blue boxes">
</div>

CSS

.checker {
    width: 100px;
    height: 100px;
    border: 1px solid black; 
    position: fixed;
    top: 0;
    
}
.boxes {
    margin-top: 300px;
    width: 600px;
    height: 600px;
}
.red {
    background: red;
}
.green {
    background: green;
}
.blue {
    background: blue;
}