In your HorizontalRule constructor, add a style property to set the height. something like this.
this.sliderLabelsRule = new HorizontalRule({
container: "topDecoration",
count: 10,
style: "height: 5px;"
}, this.getLabelsRuleDiv());
I had a similar issue where all my labels and rules where under the slider but also stacked directly on top of each other so I had ten labels and rules in one big mess, I had to set the width in the above constructor to the same width as my sliders and use position: absolute to move them into the right spot. To get them exactly where you want you may have to do something similar. Just play with the css in the style attribute of the constructor