<!-- HTML -->

<!-- You can change the style of the horizontal line like this: --> 

<hr style="width:50%", size="3", color=black>  


<!-- Or like this: -->

<hr style="height:2px; width:50%; border-width:0; color:red; background-color:red">

<!-- code -->

<hr>

<!-- code -->

var elem = document.createElement("hr");
elem.setAttribute("width", "100px");
document.body.appendChild(elem);