Instead of:

<li class="dropdown-header"><strong>Individual runs</strong></li>
<li class="dropdown-header"><strong>Average</strong></li>

We have something like this:

<li class="subsingle-header">Individual runs</li>
<li class="subsingle-header">Average</li>

And in benchmarkReport.css:

.subsingle-header {
    font-weight: bold;
}

Note: reusing the dropdown-header class or extending it is also good - I am not sure yet what's the best option. As long as we don't have the element strong any more, it's all good.

In CSS it's important to understand the difference between a "class", an "id" and a "type". In the case above the type is li, the class is subsingle-header and there is no id.

There's a CSS tutorial here (scroll down), but I haven't tried it yet:
https://www.codecademy.com/tracks/web

This is a great CSS layouting tutorial (but not really relevant for this issue):
http://learnlayout.com/