square.htm

<html>
<body>
<style>
.Border {
    margin: 20px;
    height: 800px;
    width: 800px;
    border-top: solid 1px #008;
    border-left: solid 1px #008;
  }

.Border > div {
  float: left;
  width: 49px;
  height: 49px;
  border-right: 1px solid #008;
  border-bottom: 1px solid #008;
}
.Border div div {
  text-align: center;
  padding-top: 16px;
  height: 33px;
  border: 0;
  opacity: 0;
}
.Border div div:hover { opacity: 100; }

</style>
<div class=Border>
<script>
function writeln(s) { document.write(s+'\n'); }

const BorderX = 16;
const BorderY = 16;

for (let j = 0; j<BorderY; j++) {
	for (let i = 0; i<BorderX; i++) {
		const c = '#' + i.toString(16) + j.toString(16) + '0';
		writeln('<div style="background:' + c + ';"><div>' + c + '</div></div>');
	}
}
</script>
</div>
</body>
</html>