No, the <hr /> should be in your template file (probably index.php), where you want your horizontal line to be.
Then you go to your style.css file and add these lines:
hr {color: gray; height: 1px;}
If you plan on using lots of horizontal rules with different sizes, and colors, you’ll need to add a class, like this:
In your template file: <hr class="thingrayline" />
And in your style.css file: hr.thingrayline {color: gray; height: 1px;}
That way you can use different styles of horizontal rules, giving each a different class.
