What you have there looks like a grid, which you can obtain either with many gradients on a div, either with a grid of many divs on which you apply CSS transforms.
div { box-sizing: border-box; }
.container {
overflow: hidden;
width: 32em;
height: 32em;
margin: 5.6em auto 0;
background: silver;
}
.grid {
transform: skewX(-45deg)
rotate(15deg)
scaleX(1.785) scaleY(.8)
translateX(-4.5em) translateY(-3em);
}
.grid-row {
width: 32em;
height: 2em;
}
.grid-cell {
float: left;
width: 2em;
height: 2em;
}
.high {
background: gainsboro;
}
.high:hover {
background: whitesmoke;
}<div class="container">
<div class="grid">
<div class="grid-row">
<div class="grid-cell"></div>
<div class="grid-cell high"></div>
</div>
<div class="grid-row">
<div class="grid-cell"></div>
<div class="grid-cell high"></div>
</div>
</div>
</div>
<!-- and so on... -->