Use the following code:
<script src='https://d3js.org/d3.v7.min.js'></script>
<style>
.redColor {
color: 'red'
}
.greenColor {
color: 'green'
}
</style>
<div id="demo">
<script>
let text = "";
for (let i = 1; i <= 10; i++) {
if(i<=5)
{
text += i + "<br>";
document.getElementsByTagName("TagName")[0].setAttribute("class", "redColor");
}
else
{
text2 += i + "<br>";
document.getElementsByTagName("TagName")[0].setAttribute("class", "greenColor");
}
}
</script>
</div>